Beyond “Indirect Effects” -- The Impact of Infections in

Transplantation

Jay A. Fishman, M.D.Massachusetts General Hospital

and Harvard Medical School

Viruses may be dangerous . . . .

…and not all viruses are the

same!!

The risks of viral infection: What have we been teaching?

Latent or acute “viral infection” is activated in an immunosuppressed host.

These viruses do “bad things” We call these “indirect effects” – cellular

proliferation, cytokine release, modulation of gene activity in the host, immunological effects.

What insights are gained from studies of cytomegalovirus and other viruses including Hepatitis C virus?

Cytomegalovirus

Large double-stranded DNA virus of betaherpes group with a genome size of 235 Kbp, coding more then 165 genes and over 70 viral proteins

The majority of the tegument proteins are either structural or affect the host cell or immune response to the virus

Effects of CMV in Transplantation

Viralsyndromes

Fever/NeutropeniaLiver, Heart

Lungs, RetinaGI tract, Pancreas

Adrenals, CNS

Active CMV Replication(viremia, tissue invasion)

PTLD (EBV)

Systemic immunesuppression

Cytokines, AntigensAllograft rejection

Allograft injury

Infection Graft rejection Antilymphocyteantibodies

Inflammation(cytokines, growth factors, NF-B)

Latent CMV infection: D+/R-, R+

CellularEffects

InjuryProliferation

Opportunisticinfection

Coronary VasculopathyBronchiolitis Obliterans

New PrimaryInfection

Disseminated CMV

Liver

LungKidney

Colon

Probably a misnomer Existence of indirect effects are implied based

on clinical observations, but are difficult to measure with effects of immune suppression, underlying disease, rejection→ Increased rate of opportunistic infections: Aspergillus, PCP,

acceleration of HCV infection in liver transplantation→ Probably increased graft rejection (acute and chronic)

→ Vanishing bile duct syndrome (if it exists)→ Co-factor in Bronchiolitis Obliterans Syndrome→ Accelerated atherogenesis in cardiac allografts

→ Increased EBV-associated post-transplant lymphoproliferative disorders (PTLD)

CMV: “Indirect Effects”

HCMV Protein Function

FC Receptor homologueTRL11/IRL11, UL118/119

Blocks antibody-dependent cytotoxicity; binding nonspecific antibody coating against CD8 and NK cells

Pp65 matrix Phosphorylates IE-1 protein to inhibit MHC class I-restricted antigen presentation

US3,US6, US10, US11 Block generation and export of MHC class I peptidesUS3,US6, US10, US11 Reduced expression of MHC class I peptidesUS2 Reduced antigen presentation in MHC class II pathway MHC-I homologue UL40, UL122 miRNA, UL142, UL141

Blocks NK cell activation (also: UL16, pp65)

UL18 MHC class 1 homologue; reduced immune surveillanceUL20 T-cell receptor homologue; reduced antigen presentationIE86 Inactivates p53; increase smooth muscle proliferationUL33, UL33, UL78, US27,

US28Transmembrane proteins chemokine receptors; reduced

interferon and chemokine effects; reduced inflammation, increased viral dissemination

IL-10 homologue UL111a;IL8 CXC-1 UL146, UL147

Immunosuppression; reduced MHC class I/II expression and lymphocyte proliferation; increased neutrophil chemotaxis; reduced dendritic cell and monocyte chemotaxis and function

UL144 TNF receptor homologueUL36, UL37 Anti-apoptosis for infected cells

CMV “Indirect Effects”: Many Mechanisms are CMV-specific

Upregulation of MHC class II antigens and homology between CMV IE antigen and MHC class-I (HLA-DR, Fujinami RS, et al. J Virol. 1988;62:100-105. S. Beck, Nature. 1988;331:269-272)

Block of CD8+ (MHC class I) recognition of CMV Blocks CMV antigen processing and display (immediate

early Ag modification, poor allo-T-cell CTL response) Increased ICAM-1, VCAM, cellular myc & fos (adhesion) Inversion of CD4/CD8 ratio (Schooley 1983, Fishman 1984)

Increased cytokines: IL-1, TNF, IFN, IL-10, IL-4, IL-8, IL-2/IL-2R, C-X-C chemokines and IL-8 (Kern et al, 1996; CY Tong, 2001)

Increased cytotoxic IgM (Baldwin et al, 1983)

Stimulation of alloimmune response by viral proteins (Fujinami et al, 1988, Beck et al, 1988)

Increased PDGF, TGF; autoantibodies Increased granzyme B CD8+ T-cells, -T-cells

Opportunistic Infections Promoted by CMV Infection in Transplant Patients

Fungal infections →Aspergillus spp→Pneumocystis carinii (jirovecii)→Candidemia and intra-abdominal infection after

liver and pancreas transplants Bacteremia: Listeria monocytogenes Epstein-Barr virus infection (RC Walker et al, CID, 1995, 20:1346-55),

HHV6/7, HHV8/KSHV HCV: risk for cirrhosis, fulminant HCV hepatitis,

retransplantation, mortality

Effect of anti-CMV prophylaxis on concomitant infections

0.31

0.65

0.27

0.0

0.2

0.4

0.6

0.8

1.0

Placebo/notreatment

Herp. Simplex,Varic. Zoster

Bacterialinfections

Protozoalinfections

Rela

tive r

isk

-73% -69%-35%

Hodson EM et al. Lancet 2005; 365: 2105

Pneumocystis

Preemptive Therapy vs ProphylaxisMeta-Analyses: Impact on CMV Disease

Relative Risk of CMV Disease

Study Author Preemptive Therapy Antiviral Prophylaxis

Hodson et al.0.29

(0.11–0.80)

0.42

(0.34–0.52)

Kalil et al.0.28

(0.11–0.69)

0.20

(0.13–0.31)

Small et al.0.30

(0.15–0.60)

0.34

(0.24–0.48)

Hodson EM, et al. Cochrane Database Syst Rev. 2008;(2):CD003774. Kalil A, et al. Ann Intern Med. 2005;143:870-880.Small LN, et al. Clin Infect Dis. 2006;43:869-880.

Statistically significant risk reduction of mortality with universal prophylaxis (Kalil et al) and all cause mortality (Hodson et al).

Mortality: universal prophylaxis vs. pre-emptive therapy

-38%

-6%

-60%

-50%

-40%

-30%

-20%

-10%

0%

Prophylaxis Pre-emptiveM

ort

alit

y:

risk

reduct

ion (

%)

Kalil AC et al. Ann Intern Med 2005; 143: 870; Hodson EM et al. Lancet 2005; 365: 2105

p=0.032p=ns

CMV and Graft Dysfunction: Renal CMV Disease causes poor renal graft function at

6 mos and CMV & HHV6 are associated with chronic dysfunction (3 yrs) (CY Tong et al, Transplant. 2002, 74:576-8)

Acute but not Chronic allograft rejection is reduced by CMV prevention in liver and kidney (D+/R-) Tx (D Lowance et al, NEJM 1999, 340:1462-70; E. Gane et al, Lancet 1998, 350:1729-33)

HHV6 increases CMV infection and OI’s and possibly some acute rejection in renal (A. Humar,

Transplant 2002, 73:599-604) & liver recipients (JA DesJardin CID 2001, 33:1358-62; PD Griffiths et al, J Antimicrob Chemother, 2000, 45 sup 29-34)

HHV7 associated with increased CMV infection and with acute rejection (IM Kidd et al, Transplant 2000, 69:2400-4)

Anti-CMV prophylaxis is associated with increased renal graft survival at 4 years (p = 0.0425)

100

90

80

70

60

50

0

Oral ganciclovir prophylaxis

IV pre-emptive therapy

Fre

edo

m f

rom

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ft lo

ss;

un

cen

so

red

fo

r d

ea

th (

%)

1 2 3 4Time after transplantation (years)

Kliem V, et al. Am J Transplant 2008; 8:975-83.

p value (Log rank test) = 0.0425

Prophylaxis reduced CMV

infection by 65% (p < 0.0001)

CMV and Graft Dysfunction: Liver

CMV infection is associated with cirrhosis, graft failure, retransplantation, and death in liver recipients (KW Burak et al, Liver Transplant 2002, 8:362-9)

Increased HCV recurrence and fibrosis after OLTx (partially due to HHV6) (A. Sanchez-Fueyo et al, Transplant 2002, 73:56-63; N Singh et al, Clin Transplant 2002, 16:92-6; HR Rosen et al, Transplant 1997, 64:721; R. Patel et al, Transplant 1996, 61:1279)

Possible roles of immune suppression, CMV-induced immune suppression & HCV, CMV-induced TGF/fibrosis

CMV in Heart & Lung Transplantation

Obliterative bronchiolitis (BOS) increased in: CMV serologic R+ and D+ combinations CMV infection raises OB to ~60% (Zamora MR. TransID 2001; 3: 49-56 and Am J Tx 2004, 4:1219-1226)

CMV disease and D+/R- status are associated with chronic rejection, bacterial and fungal pneumonia, OB and death in Lung Tx (SR Duncan 1992; NA Ettinger 1993; K Bando 1995; RE Girgis 1996; RN Husni 1998)

Reduction in BOS and fungus with iv ganciclovir (SR Duncan et al, Am J Crit Care Resp Dis 1994, 150:146-152; DR Snydman NEJM 1987, 317:1049-1054; JA Wagner et al Transplant 1995, 60:1473-7; HA Valantine et al, Circulation 1999, 100:61-6; HA Valentine et al, Transplantation 2001, 72:1647-1652)

CMV and Graft Dysfunction: Heart

CMV is associated with coronary allograft vasculopathy (MT Grattan et al, J Am Med Assoc 1989,261:3562-6)

Prophylaxis using CMVIg with ganciclovir reduces cardiac transplant vasculopathy (HA Valantine et al, Circulation 1999, 100:61-6; HA Valentine et al, Transplantation 2001, 72:1647-1652)

CMVIG plus DHPG reduced CMV incidence, rejection, and death vs. DHPG alone

Coronary Tx vasculopathy reduced Lung and heart-lung recipients had less OB,

better survival, fewer infections Less PTLD in double Rx

Summary: Effects of Antiviral Agents on Allograft Injury

Valacyclovir in kidney recipients 50% in rejection

Oral ganciclovir in heart, liver, kidney recipients trend in rejection

Prophylactic IV ganciclovir in heart recipients long-term benefit in of vasculopathy

Lowance D, et al, for the International Valacyclovir Cytomegalovirus Prophylaxis Transplantation Study Group. N Engl J Med. 1999;340:1462-1470.Valantine HA, et al. Circulation. 1999;100:61-66.Ahsan N, et al. Clin Transplant. 1997;11:633-639.

How best to impact indirect effects? Does prophylaxis delay or prevent CMV infection and

disease? - Yes (M Halme Transplant Int 1998, S499-501; JL Kelly et al, Transplant

1995, 59:1144-7) Does prophylaxis delay or prevent CMV-mediated

effects? Role of CMV may be uncertain but clinical data support this concept.

Do we need to prevent other viral infections? Yes How to best use “screening tests” depends on goal of

therapy - prevent CMV disease vs. asymptomatic infection & presumed indirect effects?

What is the optimal regimen? Need further data.

Mechanisms: Monocytes, Dendritic Cells In vitro, CMV infection of human monocytes results in a transient

block in the cytokine-induced differentiation of monocytes into functionally active CD1a-positive dendritic cells. Dendritic cells are potent professional antigen presenting cells and play a central role in generation and maintenance of primary T-cell responses against viral infections.

Depressed immunological functions include: impaired ability to mature in response to LPS. reduced phagocytic capacity Reduced migration in response to chemoattractant factors

RANTES, MIP-1, and MIP-3. This inhibition was mediated by early viral replicative events, which significantly reduced the cell-surface expression of CC chemokine receptor 1 (CCR1) and CCR5 by receptor internalization.

CMV infection induces secretion of inflammatory chemokines, chemokine ligand 3 (CCL3), macrophage inflammatory protein-1 (MIP-1 ), CCL4/MIP-1ß, and CCL5/regulated on activation, normal T expressed and secreted (RANTES)

HCMV-infected cells express high levels of the costimulatory molecule CD86

HCMV-infected CD1a-negative cells are unable to induce a T-cell response.

S. Gredmark and C. Söderberg-Nauclér*Journal of Virology, October 2003, p. 10943-10956, Vol. 77, No. 20

How do the effects of CMV compare with those of HCV?

HCV reinfection is universal after liver transplantation

What is the impact on the risk for other infections?

Hepatitis C

Hepatitis C virus (HCV) is a small (55–65 nm in size) enveloped, positive-sense, single stranded RNA virus of the family Flaviviridae

The genome consists of a single open reading frame of 9600 bp. The gene product and proteins are largely required for replication and infection.

Non-A Non-B Hepatitis – the early years27/42 patients with hepatic dysfunction had life-threatening infection (64.3% vs. 20% in patients without hepatitis, p<0.01))

LaQuaglia MP et al. Transplant. 32(6):504-7, 1981 Dec

Increased infections in liver transplant recipients with recurrent hepatitis C virus hepatitis Singh N et al. Transplantation. 61(3):402-6, 1996 Feb 15.

Major infections

Episodes of major infection (mean)

Recurrent infection

Bacterial Infection

Fungal Infection

CMV Late Infections

Recurrent HCV

64% (14/22)

1.45 45%, 10/22

41% 18% 32% 27%

No HCV 38% (30/78)

0.51 10%, 8/78 28% 6% 9% 6%

P = 0.04P = .003

P = 0.005 P = NS P = 0.10 P = 0.012

P = 0.09

Rejection episodes occurring within 6 months after transplantation were also higher in patients with recurrent HCV hepatitis (P = 0.09).

HCV in renal recipients

Kaplan-Meier estimate of the cumulative probability of death due to sepsis in HCV + and - kidney recipients Compared with recipients without anti-HCV before transplantation, the relative risk of graft loss among recipients with anti-HCV before transplantation was 1.30 (0.66-2.58), the relative risk of death was 2.60 (1.15-5.90), the relative risk of death due to sepsis was 6.30 (1.99-20). Bouthot BA et al. Transplantation. 63(6):849-53, 1997.

Outcomes: Outcomes in hepatitis C virus–positive recipients (compared with hepatitis C virus–negative recipients) of solid organ transplantation (non-liver)

Type of transplant Outcome

RenalDecreased long-term patient survival (follow-up >10 y)Decreased graft survivalDe novo or recurrent glomerulopathyCirrhosisPosttransplant diabetes

Pancreas, kidney-pancreas Increased proteinuria

Higher requirements for hypoglycemic agentsNo difference in patient, graft survival in short-term studiesNo long-term studies

Cardiac or lung No difference in patient, graft survival in short-term studiesNo long-term studies

Wells JT. Lucey MR. Said A. Clinics in Liver Disease. 10(4):901-17, 2006 Nov.

Post-transplant Diabetes Mellitus (PTDM) In Liver Transplant Recipients: Temporal Relationship With Hepatitis C Virus Allograft Hepatitis and Impact On Mortality The prevalence of PTDM was significantly higher in

HCV (+) than in HCV (-) patients (64% vs. 28%, P0.0001). Development of PTDM is an independent risk factor for mortality (hazard ratio 3.67, P<0.0001). The cumulative mortality in HCV (+) PTDM (+) versus HCV (+) PTDM (-) patients was 56% vs. 14% (P0.001).

PTDM associated with HCV recurrence did much worse (by 6.5 fold) than those with PTDM but without or prior to HCV hepatitis in graft.

Normalization of liver function tests with improvement in viremia was achieved in 4 of 11 patients, who demonstrated a marked improvement in their glycemic control. Between 1991 and 1998, of 185 OLTs performed in 176 adult patients, 47 HCV (+) cases and 111 HCV (-) controls. (Transplantation 2001; 72: 1066–1072)

HCV and post-transplant diabetes Mechanisms underlying diabetogenicity of HCV are

complex: Insulin resistance caused by liver injury (increased

expression of both insulin receptors and insulin receptor substrate-1)

Inhibitory actions of the virus on insulin regulatory pathways in the liver (downstream signaling through phosphoinositide-3 kinase was decreased in HCV+ liver cells)

Effects of immunosuppressive drugs, e.g., tacrolimus. Glucose dysregulation is an important determinant of

increased morbidity and mortality in liver and kidney recipients.

Lecube A, et al. High prevalence of glucose abnormalities in patients with hepatitis C virus infection: A multivariate analysis considering the liver injury. Diabetes Care 2004; 27: 1171–1175.Aytug S, et al. Impaired IRS-1/PI3-kinase signaling in patients with HCV: A mechanism forincreased prevalence of type 2 diabetes. Hepatology 2003; 38:1384–1392.Masini M, et al. Hepatitis C virus infection and human pancreatic b-cell dysfunction. Diabetes Care 2005; 28:940–941. Bloom RD. Lake JR. Am J Transplant. 6(10):2232-7, 2006 Oct.

HCV

Diabetes

CalcineurinInhibitorsIncreased Replication

Decreased CNI metabolism

Hepatic Injury

Possible anti-HCV Cyclosporine Effect?

Steroids

PTDM is a risk factor for post-transplant infection in HCV+ liver recipients (HR=7.18)

Cause of Death in HCV + patients with Infection (N=10) Pneumonia, sepsis with Pseudomonas, Enterococcus,

Torulopsis, and Candida Enterobacter sepsis Pneumocystis carinii pneumonia with ARDS Sepsis with VRE, Torulopsis, and Pseudomonas infection Sepsis with Klebsiella and Candida Pneumonia with multiorgan failure, Candida, Aspergillus Pneumocystis carinii pneumonia with disseminated

Aspergillus Aspiration pneumonia with ARDS and Candidemia Klebsiella pneumonia with ARDS Cryptococcus pneumonia with ARDS

How about HCV and Immune Function?Progression to chronic hepatitis C appears to be related

to exhaustion of adaptive immune function. Containment of HCV infection requires a coordinated, vigorous, and sustained multispecific CD4+ and CD8+ T-cell responses to the virus. (Spangenberg HC et al. Intrahepatic CD8+ T-cell failure during chronic hepatitis C virus infection. Hepatology 2005;42:828-37; Nellore, A and Fishman JA. NK Cells, Innate Immunity and Hepatitis C Infection after Liver Transplantation. Clin Infect Dis. 2011, 52 (3): 369-377)

HCV infection may enrich the hepatic regulatory T cell population which may persist after liver transplantation. Compared to uninfected recipients, OLT recipients with HCV have enhanced peripheral Foxp3+ CD4+CD25+ T cell population. The mechanisms are uncertain. (Ciuffreda D et al. Liver Transpl 2010;16:49-55; Carpentier A et al. Increased expression of regulatory Tr1 cells in recurrent hepatitis C after liver transplantation. Am J Transplant 2009;9:2102-12.)

HCV is associated with decreased numbers of peripheral dendritic cells in patients with chronic and post-transplant HCV infection.

Are some mechanisms underlying increased risk for infection shared between “viruses”?

Heterologous immunity

Heterologous immunity: Immune memory responses to previously encountered pathogens which alter subsequent immune responses to unrelated pathogens or grafts. Responses may be mediated by TNFα, IFNγ In some cases:

Memory CD4+ cells mediate bacterial virus cross reactivity

CD8+ cells mediate virus virus cross reactivity

Heterologous Immunity and Viral Infection Increased rejection

Virally-induced alloreactive memory may create a barrier to transplantation tolerance or induce graft rejection or autoimmunity (AB Adams et

al, JCI 2003:111:1887-95) Alloreactive T-cells are activated by viral infections

(Yang H and Welsh RM JI 1986: 1186-1193; Braciale TJ et al J Exp Med 1981, 153:1371-76; Chen HD 2001, Nat Imm 2:1067-76)

Allo-cross reactivity of CMV and EBV (Adams AB et al. Immunol Rev 2003, 196:147-160.)

Pre-existing alloreactive memory T-cells increase rejection rate (Heeger PS et al. JI 1999, 163:2267-75)

Differences by virus type, persistence, latency?

Rejection and treatment increase viral replication and risk for opportunistic

infection.

Heterologous Immunity T-cell responses to viral epitopes occur in a distinct

hierarchy for a given virus on a given MHC background (“public specificity”)

The hierarchy of T-cell responses are governed by the competition between epitopes for presentation by MHC, the availability of nontolerized T cells capable of responding to the epitopes, and the competition between T cells binding to domains on the antigen-presenting cells (Yewdell JW, Bennink JR: Annu Rev Immunol 1999, 17:51-88.)

Due to elevated frequencies of antigen-specific memory T cells and their elevated activation state, infection of a host with a virus that encodes an epitope cross-reactive with that memory pool might recruit those T cells into a vigorous immune response but would suppress responses to other epitopes. (Brehm MA et al. Nat Immunol 2002, 3:627-634; Klenerman P, Zinkernagel RM: Nature 1998, 394:482-485.)

Heterologous Immunity

Can create gaps in immunity to subsequent pathogens with shared but non-protective epitopes?

Process is dependent on the sequence of infections and can be either beneficial or detrimental to the host

T-cell depletion or Stem cell transplants for tolerance

Homeostatic proliferation to self-MHC-peptide complexes: In process of repopulation, T-cell repertoire (TCR) may be narrowed to reflect memory (prior exposures) but may not respond well to new, subsequent exposures (SJ Lin Blood. 112(3):680-9, 2008; M Cornberg J Clin Invest. 116(5):1443-56, 2006)

Broader Concepts: The Interface of Innate and Adaptive Immunity

Toll-Like Receptors (TLRs) are pattern recognition receptors

Promote allograft rejection via signal transduction (usually MyD88 and/or Trif) pathways – ligands may include products of cellular damage (damage-associated molecular patterns, DAMPs) or inflammation

Likely designed for microbial products – so more bacteria, viruses, fungi, or nucleic acids more stimulation and

So dirty surgery, vascular catheters left in too long, viral activation …. TLR activation

Heat Shock proteins, extracellular matrix

proteins, collagens, β-defensin, nuclear protein HMGB1,

oligonucleotides, DNA, RNA, …

TLR-ligation can block tolerance induction

Tissue inflammation (infection, surgery) and injury trafficking of T-cells

Listeria monocytogenes (intracellular bacterium) IFNβ blocks heart and skin tolerance (T Wang et al, AJT, 10:1524, 2010)

Staphylococcus aureus (but not Pseudomonas aeruginosa) IL-6 (EB Ahmed et al, AJT, 11:936, 2011)

Newcastle disease virus IFNα by dendritic cells (DC) and macrophages (Y Kumagi et al, Immunity, 27:240, 2007)

Mechanism: Non-specific stimulation (cytokines, chemokines) of T-cells or increased antigen presentation by APCs?

Natural Killer Cells induce Coronary Allograft Vasculopathy (CAV) in Mice without T- or B-cells if infected with Lymphocytic Choriomenigitis Virus

Parental C57BL/6.RAG1-/- (H2Db) hearts were transplanted into (C57BL/6 x BALB/c.RAG1-/-) F1 (H2Dbxd) recipients. Recipients were sacrificed on post-operative day 56 with beating hearts.

Mice were infected IP with 2.25 x 10e5 PFU of LCMV Armstrong strain. Infected hearts had a mean of 518,725 copies of LCMV per nanogram tissue RNA.

LCMV inoculation alone: 6 of 8 recipients infected with LCMV developed florid CAV lesions.

Controls: viral media injection 1 in 15 developed lesions of CAV

LCMV inoculation with anti-NK1.1 mAb administration to deplete NK cells. None of the 6 mice infected with LCMV and treated with anti-NK1.1 mAb developed CAV.

Conclusion: NK cells appear to mediate the development of CAV induced by LCMV infection.

NK Cells, LCMV Infection:

B6.RAG1-/- into CB6F1.RAG1-/-

a. No infection

b. Control

c. Isograft

d. Day 28 LCMV

e. Day 56 LCMV

f. NK Cell depleted

g. NK Cell infiltrate

h. Smooth muscle cell proliferation

i. Macrophages

Let’s focus for a moment on the likely purpose of the immune system

• The human microbiome refers to the community of microorganisms, including prokaryotes, viruses, and microbial eukaryotes, that populate the human body.

• From an initial genome sequencing project at NIH of 178 microbial genomes – 547,968 predicted polypeptides that

correspond to the gene complement of these strains

– 30,867 polypeptides, of which 29,987 (approximately 97%) were previously unidentified ("novel") polypeptides from the microbiome of the gastrointestinal tract

• Simple math – there are 100 trillion organisms in the GI tract. It is likely that humans were developed to support bacterial growth!!

Science. 2010 May 21;328(5981):994-9.

•Phylogenetic tree of human 16S rDNA sequences Organisms sequenced as part

of the Human microbiome project are highlighted in blue.

The Gut Microbiome

Colon contains >1010-11 cfu commensal bacteria/gram tissue. Note: >1000 different microbial species from >10 different divisions colonize the GI tract, but just two bacterial divisions—the Bacteroidetes and Firmicutes—and one member of the Archaea appear to dominate, together accounting for >98% of the 16S rRNA sequences obtained from this site.

Role of regulatory T cells in tolerance to commensal bacteriaChyi Hsieh, Washington University, St. Louis

The colonic microbial and Treg TCR repetoires are unique and may play central roles in the pathogenesis of autoimmunity, inflammatory bowel disease, and in determination of immunity to self and non-self antigens

Likely includes “sampling” of GI flora by dendritic cell processes presentation

Depletion

Naïve T cells Memory T cells

Fast Homeostatic Proliferation

Slow Homeostatic Proliferation

Memory T cells

Memory T cells

Lymph nodes

Gut

Spleen

From: Tchao and Turka, AJT 2012; 12: 1079–1090

IL-7/MHC

Costimulation + Commensal bacteria

Which antigens drive or control homeostatic proliferation?

Does T-cell depletion and reconstitution or costimulatory blockade in the face of cross-

reacting antigen alter immunity to the graft and reduce immune competence?

Infection and Transplantation

Pre-Transplantation•Organ dysfunction•Colonization (ICU)• Antimicrobials• Infections• Vaccination

Transplant Surgery• Infection (technical)• Tissue injury • Organ dysfunction

Post-Transplantation•Depletion and Immune reconstitution•Immunosuppression•Community exposures•Opportunistic infection

Immune memory • Heterologous or cross-reactive• Narrowed immune responses •Stimulation by “Latent or persistent infections”

• Ligands for Pattern recognition receptors cytokines, chemokines

•Pathogen & Allograft derived antigens• Damage-associated molecular patterns

• Alloimmune stimulation decreased tolerance• Enhanced antigen presentation

• Heterologous or cross-reactive memory

Rejection• Failed costimulatory blockade

• Narrowed immune responses (infections)• Stimulation by new or “persistent infections” (graft injury) cytokines, chemokines• Increased effector over Treg cells

Remaining Questions Do chronic viral infections diminished responses to

new antigens and risk for opportunistic infections via compression of the T-cell repertoire?

How much virus/replication is needed for various effects? Role of asymptomatic viral replication?

Altered response to subsequent cross-reacting infections: Suppression by regulatory T-cells Excessive cytokine responses Chronic cytokine release bias of T-cells to effector and

fewer memory cells (lower quality memory responses) Do vaccines make this process worse? Role of innate immune function (NK and plasmacytoid

dendritic cells, other subpopulations) Homeostatic proliferation: Do we provoke graft rejection

by altering gut flora or antiviral prophylaxis?

If I can help: jfishman@partners.o

rg

Thank you for inviting me. I would be happy to answer questions.