Adoptively Transferred Central Memory Derived Human CD8+Effectors Exhibit Superior Engraftment Fitness Over Their Naïve T Cell Derived Counterparts

Abstract 2982

In clinical trials of adoptive T cell therapy, the persistence of transferred cells correlates with therapeutic efficacy. The engraftment fitness of ex vivo propagated T cells is in part pre-determined by the differentiation status of precursor T cells from which effector cell products are derived. In peripheral blood, T cells are comprised of three major subsets- naïve, central memory (Tcm) and effector memory (Tem), each having distinct phenotypic and functional attributes. We have previously shown that human CD8+ effector cells derived from Tcm were superior to Tem in their ability to engraft and persist following adoptive transfer (Wang, X. 2011). In this study, we set out to compare the engraftment fitness of CD8+ effector cells derived from naïve precursors with that of Tcm-derived effectors. FACS sorted CD8+ CD45RA+CD62L+ naïve (Tn) and CD8+CD45RO+CD62L+ Tcm cells from healthy donors were expanded in vitro for 14 days in the presence of OKT3, feeder PBMC and IL-2 at 50U/mL. Despite the comparable levels of CD28 expression on unstimulated CD8+ Tn and CD8+Tcm (91±2% for CD8+Naive and 94±2% for CD8+Tcm), Tcm-derived effector T cells (CD8+TCM/E) displayed significantly higher levels of CD28 expression with corresponding high levels of cytoplasmic phosphorylated-AKT as compared to Tn-derived cells (CD8+TN/E) (47±5% for CD8+TN/E vs. 83±4% for CD8+ TCM/E). After the initial 14 days of in vitro expansion, CD8+TCM/E were able to persist in vitro for more than 50 days in the presence of gamma-c cytokines (IL-2 50/ml or IL-15 10ng/ml) while CD8+TN/E failed to survive in either condition, which is consistent with the observed higher expression levels of IL-15R α and IL-2R β by CD8+TCM/E. After engraftment in huIL-15 replete immunodeficient (NSG) mice, we observed that CD8+TCM/E exhibited higher levels engraftment and mounted more robust proliferative responses to in vivo challenge with immunostimulatory vaccines. In contrast to CD8+TN/E, engrafted CD8+TCM/E reaquired/sustained high frequency of cells expressing IL-7Ralpha. To re-direct T cell specificity against B-lymphoid malignancies, purified CD8+Tn and CD8+Tcm from healthy donors were engineered with lentiviral vector encoding CD19R-CD28-EGFRt-epHIV7. CD19-specific CD8+TCM/E persist after adoptive transfer into the human IL15 reconstituted NSG mice, whereas no engraftment was detected in the CD19-specific CD8+TN/E infused NSG mice. These studies using human T cells support the use of central memory derived effector cells for adoptive therapy of cancer and infectious disease.