Cryptic leukemia antigens share homology with microbial epitopes and stimulate T-cell responses in healthy donors

Leukemia cells express cryptic tumor-specific antigens (TSAs) derived from aberrantly transcribed non-exomic genome sequences. These antigens are generally absent from healthy tissues yet shared across patients, making them attractive immunotherapy targets by minimizing on-target/off-tumor toxicity while offering broad applicability. However, their immunogenic potential and the nature of the T-cell repertoire they stimulate remain unknown. Cryptic antigen-specific CD8+ T cells could be expanded from healthy donor T-cell repertoires for six out of nine candidate acute leukemia cryptic TSA. T-cell receptor (TCR) and epitope sequence analysis revealed oligoclonal or near-monoclonal responses, involving shared and donor-restricted clonotypes recognizing cryptic TSAs which shared sequence homology with microbial epitopes. Orthotopic TCR replacement with cryptic TSA-specific TCR chains using a one-step CRISPR-Cas9 approach further validated the antigenic specificity and therapeutic potential of two TCRs respectively targeting cryptic TSAs from acute myeloid and lymphoid leukemia. To our knowledge, this is the first report describing functional TCRs directed against cryptic leukemia TSAs and highlights their potential as a new class of antigens for T-cell-based immunotherapies. Key pointsO_LIA high proportion of cryptic leukemia TSAs shares homology with microbial epitopes and can stimulate expansion of low-frequency T cell repertoire in healthy individuals. C_LIO_LIEx vivo expansion of cryptic TSA-specific T cells enables TCR identification that can be used to devise new T cell immunotherapies. C_LI Visual Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=122 SRC="FIGDIR/small/691479v1_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@1bd720dorg.highwire.dtl.DTLVardef@8ac6d6org.highwire.dtl.DTLVardef@104289aorg.highwire.dtl.DTLVardef@5a65e_HPS_FORMAT_FIGEXP M_FIG C_FIG ConclusionCryptic leukemia antigens elicit antigenic and specific T-cell responses and represents novel targets for TCR or BiTE immunotherapy.