Mantle cell lymphoma (MCL) is among the most aggressive B cell lymphomas with median patient survival of only 3–4 years. Although high dose therapies followed by hematopoietic stem cell transplantation is an option for therapy, it is difficult to successfully treat MCL until the therapeutic strategy is developed to target and eliminate the residual/relapsing tumors after existing chemotherapies. Therefore, characterization of these residual/relapsing tumor cells after chemotherapy as a basis for developing therapeutic strategy to target residual/relapsing MCL cells is essential. Accordingly, we have isolated the residual/relapsing tumor cells by transplanting the human MCL cell line, Granta519, into NOD-SCID mice followed by CHOP+Bortezomib chemotherapy. Isolated residual/relapsing tumor cells from liver and kidney characterized morphologically using microscopy, and immunophenotypically for CD45, CD19 and CD23 expression by flow-cytometry showed no differences. However these cells had a significantly higher growth rate and increased chemo-resistant potential in vitro as determined by MTT and 3[H]-thymidine incorporation assay compared to parental Granta cells. In addition, NOD-SCID mice transplanted with cells isolated from liver had significantly shorter survival compared to parental cells indicating a higher tumorigenic potential of relapsed tumor cells pre-exposed to chemotherapy. There was a higher frequency of side population (SP) cells in relapsed tumor cells compared to parental cells as determined by flow cytometry after Hoechst staining. In addition, there was an increased expression of transcripts associated with maintenance of stem cells, including GLI transcription factors, targets of hedgehog signaling, as determined by microarray and confirmation by real time PCR, suggesting that increased stem cell-like cells in the relapsing tumors may be responsible for the chemo-resistance and increased tumorigenic potential. However, these residual/relapsing cells were susceptible to in vitro generated MCL-specific cytotoxic T lymphocytes (CTLs) against parental cells. We have demonstrated the potential of inhibition of GLI to render the MCL cells sensitive to chemotherapy (

Hegde et al.,
Mol Cancer Ther
). Therefore, we have developed a strategy of targeting hedgehog signaling mediators such as GLI transcription factors using GLI-antisense oligonucleotides or the proteosome using Bortezomib, to target residual/relapsing tumor cells after CHOP chemotherapy followed by tumor-specific adoptive T cell therapy (ATT) against human MCL using the mouse model. There was a significantly improved survival and decreased tumor burden in the mice treated with CHOP+GLI-ASO+ATT or CHOP+bortezomib+ATT compared to CHOP only treated controls suggesting the potential of targeting of residual/relapsing tumor cells using this strategy. Together, these results demonstrate the potential of this novel combined therapeutic strategy against human residual/relapsing MCL, which may have future clinical application.

Conflict of interest: None; Funding: Lymphoma Research Foundation, New York, NY.

Disclosures: No relevant conflicts of interest to declare.

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