250-OR: Hypoproliferative CD8 Effector Memory (EM) Subsets Are Linked to Preservation of C-Peptide in Alefacept-Treated Recent-Onset Type 1 Diabetes (T1D) Subjects

In the ITN T1DAL trial, alefacept (LFA3-Ig fusion protein) preserved endogenous insulin production in 30% of recent onset T1D patients for two years after therapy. Although patients experienced immune alterations following treatment, including depletion of CD2hi effector T-cells and preservation of CD2lo regulatory T-cells, these effects were not predictive of overall response or outcome. However, using an unbiased approach and a combination of flow cytometry, RNA-sequencing, and CyTOF, we were able to identify a CD8 T-cell signature of response at ∼two years following treatment. Preservation of C-peptide was associated with a large transcriptional module (n= 738 genes; R= 0.4, p= 0.023) including activation and exhaustion-associated genes identified at two years following treatment using WGCNA. This module was further dissected into two distinct CD8 EM populations through correlation with hierarchically gated and clustered cytometry data. While both populations expressed multiple inhibitory receptors (IR) (TIGIT, KLRG1, T-bet, EOMES) and were hypo-responsive in in vitro proliferation assays, they were distinguished by higher expression either of markers seen in cytotoxic and terminally differentiated effector T cells (CD57+ Granzyme B+) or of PD-1. Gene expression signatures of both the CD57 and PD-1 subsets significantly overlapped with a previously identified partial exhaustion signature (p= 0.005, for both subsets). Our findings demonstrate an association of partially exhausted memory CD8 T-cells with beneficial clinical response to alefacept as we observed previously with teplizumab (anti-CD3) treatment. Our findings also demonstrate linkage of two phenotypically distinct IR-high, hypo-proliferative CD8 EM T-cell subsets with beneficial response. Together, our findings suggest that pathways regulating proliferation of EM CD8 cells may lead to successful immune interventions for T1D. Disclosure E. Serti: None. K.E. Diggins: None. V.S. Muir: None. T. Lu: None. E. Balmas: None. G.T. Nepom: None. S. Long: None. P. Linsley: Consultant; Self; Bristol-Myers Squibb. Funding National Institute of Diabetes and Digestive and Kidney Diseases/National Institute of Allergy and Infectious Diseases (UM1AI109565)