Comparative Analysis Of Phenotypic And Functional Attributes Of Antigen-Specific Naïve And Memory T Cell Subsets Potentially Affecting The Efficacy Of Adoptive T Cell Therapy

Abstract

The quality of the T cells that are selected for expansion and adoptive transfer has been identified as a critical factor that determines the persistence, and therefore, efficacy, of transferred cells. The memory T-cell compartment is heterogeneous and encompasses multiple T cell subsets with divergent properties. Latent human cytomegalovirus (CMV) infection is controlled by a limited repertoire of immunodominant T cells specific for viral peptides. The antigen-specific T cell subsets responsible for maintaining memory T cells and repopulating them in response to periodic viral reactivations are not well characterized. In the first chapter of my thesis work, I developed a human xenograft model in NOG mice to conduct comparisons of CMV-specific TCM and TEM derived cells in vivo, when administered together with the cytokine IL-2 or IL-15. These studies specifically compared CMVpp65 specific TCM and TEM derived cells as to their capacity to selectively target, accumulate in and induce inhibition of human colon carcinoma xenograft transduced to express CMVpp65. The experiments also evaluated the kinetics and level of T-cell accumulation in these targets and their persistence both in the xenografts and other tissues, particularly the marrow. In the second chapter of my thesis work, I focused on identifying the most effective T-cell memory population that would provide higher in vivo proliferation, survival, and overall functional activity. The studies comparatively evaluated CMVpp65 epitope-specific tetramer+ T-cell populations within the memory T-cell compartment as to their origins, phenotype, functional attributes, T-cell clonal diversity, proliferation and survival. In the third chapter of my thesis work, I evaluated the differential functional activity of low and high affinity chimeric antigen receptor constructs encoding T-cell receptor mimics specific for an immunogenic peptide of an oncognic protein, WT-1, presented by HLA A0201. Overall, the thesis work has implications for the design of T cell-based immunotherapies. First, the studies indicate that while TCM and TEM derived T-cells exhibit differences in phenotype and in the kinetics and degree of their respective accumulations in CMVpp65+ CoCa xenografts, their antigen-specific activities and their persistence in vivo were fairly equivalent. The differences lies in the cytokine treatment: in IL-15/IL-15R? treated mice there was a more prolonged persistence of both TCM and TEM derived T-cells compared to IL-2 treated mice. Second, the studies suggested Tet+ TSCM rather than Tet+ TN are the principal reservoir for rapid repopulation of immunodominant TEM cells in the circulation. TSCM could potentially provide better disease control by facilitating early recovery of more short-lived immunodominant virus-specific TEM cells that normally control latent infection and thereby provide sustained long-term protection from disease. Finally, the studies validate the superior specific binding and HLA-restricted WT-1 peptide specific cytoxicity of T-cell expressing the high affinity CAR against HLA A0201+WT-1+ human tumor cells compared to low affinity CAR against the same antigen.