Evaluation of Human Thymic Function during Health and

Evaluation of Human Thymic Function during Health and HIV-1 Infection Ping Ye and Denise Kirschner DIMACS Workshop 9/23/2001

Outline n Thymic function in healthy people n n n Thymopoiesis Markers to represent recent thymic emigrants (RTE) Thymopoiesis model TREC model Thymic function during pediatric HIV-1 infection n n HIV-1 infection Clinical and experimental studies Thymic infection model Evaluation of TREC

The Thymus Janeway CA et al. Immunobiology 5 th ed. 2001 Haynes BF. Clin Immunol. 92(1): 3 -5, 1999

Thymopoiesis Berkowitz RD et al. J Immunol. 161(7): 3702 -10, 1998

Recent Thymic Emigrants (RTE) n n n Lack of phenotypic markers for human RTE Human RTE generally refer to T cells that have undergone only a few cellular divisions after leaving the thymus T cell receptor excision circles (TREC) have recently been used as a measure of the number of RTE

T Cell Receptor Excision Circles (TREC) Pieces of DNA fragments that are generated during TCR gene rearrangement in the thymus and then exported from the thymus to periphery within T cells episomally Janeway CA et al. Immunobiology 5 th ed. 2001 Haynes BF et al. Annu Rev Immunol. 18: 529 -60, 2000

TREC as A Measure of RTE

Parameters Estimating RTE n TREC concentration n n Naïve T cells (CD 45 RA+, CD 62 L, CD 95+) n n n Is affected by both RTE and peripheral T cell proliferation and death May have long lifespan May proliferate in an antigen-independent manner May rapidly convert to memory cells May be converted from memory cells Thymic volume n Assuming thymic volume is proportional to RTE levels

Two Questions to Address 1 st Can TREC concentration be properly used as measure of RTE? 2 nd Whether thymic infection with different HIV-1 strains contribute to differences in disease progression?

Thymopoiesis Model Cell Source THYMUS TN TES(t) ITTP DP BLOOD/ LYMPHOID TISSUES SP 4 SP 8 CD 4+ RTE CD 8+ RTE

Simulation Results for Thymopoiesis Model Thymocytes RTE/day

Model Simulation Values Compared with Experimental Data

TREC Model THYMUS SP 4 CD 4+ RTE CD 4+ T cell SP 8 CD 8+ RTE CD 8+ T cell TREC BLOOD/ LYMPHOID TISSUES TREC

Simulation Results for TREC Model Douek DC et al. Nature. 369(6712): 690 -5, 1998. Zhang L et al. J. Exp. Med. 187(11): 1767 -78, 1998

Four Events Affecting TREC Concentration THYMUS SP 4 SP 8 1 2 CD 4+ RTE CD 4+ T cell 3 4 TREC CD 8+ RTE CD 8+ T cell TREC BLOOD/ LYMPHOID TISSUES TREC concentration is affected by 1 Thymic output 2 T cell division 3 T cell death 4 TREC degradation

TREC Can Be Equally Affected by Thymic Output and T Cell Division (at Any Age) #

TREC Concentration during Aging Healthy Volunteers sj. TREC cj. TREC Age (years) Douek DC et al. Nature. 396(6712): 690 -5, 1998

Thymic Involution Induce TREC Decline (Over Entire Lifespan) TREC concentration is a good marker for RTE in healthy people

Summary Thymic Function in Healthy people n n Our model quantifies the number of RTE and TREC concentration over an 80 -year lifespan TREC concentration can be equally affected by thymic output and T cell division at any age Thymic involution induces TREC concentration decline over the entire lifespan TREC concentration is a good marker for both CD 4+ and CD 8+ RTE in healthy people

Outline n Thymic function in healthy people n n n Thymopoiesis Markers to represent recent thymic emigrants (RTE) Thymopoiesis model TREC model Thymic function during pediatric HIV-1 infection n n HIV-1 infection Clinical and experimental studies Thymic infection model Evaluation of TREC

HIV-1 Structure n n n n Associated with AIDS Retrovirus family Two identical ss RNA Enveloped virus Antigenic variation Infects CD 4+ cells Entry requires CD 4 and coreceptor

HIV-1 Entry

Classification of HIV-1 Strains n R 5 strain n n X 4 strain n n Uses CCR 5 as coreceptor Replicates slowly and is minimally cytopathic Is primarily transmitted Is prevalent in the early stage of disease Uses CXCR 4 as coreceptor Replicates fast and is highly cytopathic Is rarely transmitted Appears in approximately 50% of patients in the late stage of disease R 5 X 4 strain n n Uses either CCR 5 or CXCR 4 as coreceptor Has similar properties as the X 4 strain

HIV-1 Disease Progression Hypotheses for the decline of CD 4+ T cells in the blood n Changes in cell migration patterns n Changes in cell life-spans n Changes in cell production by the thymus

Clinical Studies of Thymic Infection with HIV-1 n n n TREC levels in CD 4+ and CD 8+ T cells decline Naïve CD 4+ and CD 8+ T cell numbers decline Thymic volume decreases The thymus undergoes morphological changes “Thymic dysfunction” (TD+) is described in a subset of vertically-infected infants

“Thymic dysfunction” (TD+) Two distinct modes of pediatric HIV-1 disease progression • • Normal progressors Fast progressors 10 years to AIDS (85%) 2 -3 years to AIDS (15%) lower CD 4+ and CD 8+ counts (Di. George Syndrome)

Experimental Studies of Thymic Infection with HIV-1 n Coreceptors n n CCR 5 CXCR 4 Expressed in low levels on DP, SP 4, SP 8 cells Expressed in high levels on ITTP, DP cells, low levels on SP 4 and SP 8 cells HIV-1 strains n R 5 strain n X 4 strain Infects DP and SP 4 cells Minimally cytopathic Infects ITTP, DP and SP 4 cells Highly cytopathic Thymocyte maturation stages n n SP 4, SP 8 ITTP, DP Support active viral replication Support less viral replication

Two Questions to Address 1 st Can TREC concentration be properly used as measure of RTE? 2 nd Whether thymic infection with different HIV-1 strains contribute to differences in disease progression?

Thymic Model With HIV-1 Infection Cell Source THYMUS TN TES(t) X 4 ITTP R 5 DPR SP 4 R SP 8 R R 5 X 4 SP 8 R 5 X 4 DP SP 4 CD 4+ RTE BLOOD/LYMPHOID TISSUES ITTPX CD 8+ RTE DPX SP 4 X SP 8 X X 4

Virtual Pediatric Thymic Infection

Simulations of CD 4+ RTE Predict Bimodal Pattern of Blood CD 4+ T Cell Counts

Simulation Values at Year Two of Virtual Infection Compared with Experimental Data

Bifurcation Parameters Implications for Treatment n n n Viral influx from blood into the thymus Virulence of strains (viral infection rate and production rate) HIV-1 induced death of uninfected thymocytes Progenitor cells from bone marrow Carrying capacity of the thymus

TREC Concentration during HIV-1 Infection HIV-1 Infected Subjects sj. TREC Age (years) Douek DC et al. Nature. 396(6712): 690 -5, 1998

Two Questions to Address 1 st Can TREC concentration be properly used as measure of RTE? 2 nd Whether thymic infection with different HIV-1 strains contribute to differences in disease progression?

T Cell Kinetics during HIV-1 Infection We include these effects in the model to represent HIV-1 infection

T Cell Counts and TREC Concentrations in HIV-1 Infected Subjects (Age 30) T cells TREC Margolick JB et al. J Acquir Immune Defic Syndr. 6(2): 153 -61, 1993 Zhang L et al. J. Exp. Med. 187(11): 1767 -78, 1998

Model Prediction for Thymic Output during HIV-1 Infection TREC concentration is a good marker for CD 4+ RTE TREC concentration is NOT a good marker for CD 8+ RTE

Summary Thymic Function during Pediatric HIV-1 Infection n n Infection with R 5 and X 4 strains induces different degrees of thymic dysfunction, which is related to CD 4+ T cell counts and disease progression as seen in pediatric patients Thymic infection in pediatric patients is more severe than in adult patients, likely due to higher viral loads and a more active thymus Suppressing viral load in blood, high drug efficacy within the thymus, and improving inherent thymic function are necessary for reconstitution of RTE levels Protease inhibitors have high levels of efficacy directly suppressing viral replication within the thymus, while reverse transcriptase inhibitors have low efficacy TREC concentration is a reliable marker for CD 4+ RTE, but not for CD 8+ RTE in HIV-1 infected subjects

Conclusions n n n Peripheral T cell turnover should be examined together with TREC concentration as a measure of RTE Infection with different HIV-1 strains induces different degrees of thymic dysfunction, contributing to CD 4+ T cell depletion and disease progression With adequate suppression of viral replication within both the blood and the thymus during HAART, thymic function recovery can reconstitute immune cell numbers

Publications n n n Ping Ye and Denise Kirschner (2002). Reevaluation of T cell receptor excision circles as a measure of human recent thymic emigrants. Journal of Immunology, 168(10), 4968 -4979. Ping Ye, Athena Kourtis, and Denise Kirschner (2002). The effects of different HIV-1 strains on human thymic function. AIDS Research and Human Retroviruses, 18(17) (In press). Ping Ye, Athena Kourtis, and Denise Kirschner. Reconstitution of thymic function in HIV-1 patients treated with highly active anti-retroviral therapy (submitted).

Acknowledgments n n n Dr. Denise Kirschner Collaborator: Dr. Athena Kourtis Dr. Ramit Mehr Kirschner lab members Funding n n NIH and Whitaker Foundation to DEK Rackham Graduate School and Elizabeth Glaser Pediatric AIDS Foundation to PY

Clinical Studies of Thymic Function during HAART n n TREC levels recover Naïve CD 4+ and CD 8+ T cell numbers increase Thymic volume increases Children with “thymic dysfunction” response well to HAART

Model of Thymic Function Reconstitution during HAART Cell Source TN THYMUS TES(t) R 5 DPR SP 8 R SP 4 R R 5 SP 4 X 4 SP 8 CD 4+ RTE ITTPX X 4 DP R 5 X 4 ITTP CD 8+ RTE DPX SP 4 X SP 8 X X 4 BLOOD/LYMPHOID TISSUES n n n Reduce viral influx into the thymus Decrease viral infection and production (if thymic drug efficacy > 0%) Decrease HIV-1 induced death of uninfected thymocytes Increase progenitor cells from bone marrow Increase carrying capacity of the thymus

Simulations of pediatric thymocyte dynamics during HAART

Simulations of CD 4+ RTE Predict HAART Agent Thymic Efficacy RTI HAART