Malekzadeh et al. show that peripheral blood lymphocytes (PBL) contain a small fraction of mutated TP53 neoantigen-reactive T cells, which was consistent with tumor-infiltrating lymphocyte response to mutant TP53. In vitro stimulation (IVS) using either p53 neoantigen long peptide or tandem minigenes, with multiple hotspot TP53 mutations, followed by 4-1BB/OX40 enrichment, increased the frequency of PBL-derived reactive T cells to as high as 70%. IVS increased the TCRB clonality in PBL-derived T cells, and IVS T cells recognized naturally presented, HLA-restricted neoantigens.
Contributed by Shishir Pant
PURPOSE: The purpose of this study was to evaluate antigen experienced T cells in peripheral blood lymphocytes (PBL) for responses to p53 neoantigens. EXPERIMENTAL DESIGN: PBLs from patients with a mutated TP53 tumor were sorted for antigen-experienced T cells and in vitro stimulation (IVS) was performed with p53 neoantigens. The IVS cultures were stimulated with antigen-presenting cells expressing p53 neoantigens, enriched for 41BB/OX40 and grown with rapid expansion protocol. RESULTS: T-cell responses were not observed in the PBLs of 4 patients who did not have tumor-infiltrating lymphocyte (TIL) responses to mutated TP53. In contrast, 5 patients with TIL responses to mutated TP53 also had similar T-cell responses in their PBLs, indicating that the PBLs and TILs were congruent in p53 neoantigen reactivity. CD4(+) and CD8(+) T cells were specific for p53(R175H), p53(Y220C), or p53(R248W) neoantigens, including a 78% reactive T-cell culture against p53(R175H) and HLA-A*02:01. Tracking TCRB clonotypes (clonality, top ranked, and TP53 mutation-specific) supported the enrichment of p53 neoantigen-reactive T cells from PBLs. The same T-cell receptor (TCR) from the TIL was found in the IVS cultures in three cases and multiple unique TCRs were found in another patient. TP53 mutation-specific T cells also recognized tumor cell lines bearing the appropriate human leukocyte antigen restriction element and TP53 mutation, indicating these T cells could recognize processed and presented p53 neoantigens. CONCLUSIONS: PBL was a noninvasive source of T cells targeting TP53 mutations for cell therapy and can provide a window into intratumoral p53 neoantigen immune responses.