A tritherapy combination of a fusion protein vaccine with immune‐modulating doses of sequential chemotherapies in an optimized regimen completely eradicates large tumors in mice

Abstract

Tumor-induced immunosuppression plays a critical role in both impeding tumor-specific immune responses and limiting the effects of cancer immunotherapy. Analyses of regulatory cells recruited during the growth of the E7-expressing tumor, TC-1, revealed a high percentage of regulatory T cells (Tregs) as well as myeloid-derived suppressor cells (MDSCs) in spleens and tumors. In this study, we proposed that treatment with immune-modulating doses of cyclophosphamide (CTX) and all-trans retinoic acid (ATRA) would result in a beneficial tumor microenvironment with the suppression of Tregs and MDSCs and, thus, enhance the effect of a human papillomavirus protein vaccine. Our results showed that CTX preconditioning and persistent ATRA treatment along with the vaccine achieved long-term survival and induced long-term memory responses. However, the effect of the antitumor response sharply declined when the tritherapy was initiated after the optimal therapeutic time. The more intensive regimen could rescue the effect of the tritherapy accompanied by the decreased percentage of Tregs and MDSCs in spleens and tumors. Besides, a favorable host environment was created by the reduced secretion of interleukin-10 and 6 and vascular endothelial growth factor (VEGF) in the tumor niche and decreased the expression of phosphorylationsignal transducer and activator of transcription 3 of TC-1 tumors. Our data shed light on the immune-modulating doses of sequential chemoimmunotherapeutic strategy targeting not only the tumor but also its microenvironment, which suggests a potential clinical benefit for the immunotherapy of HPV-associated malignancies.Over the last decade, despite several promising reports with a vaccine approach for some cancer patients, consistent clinical responses have not been very well obtained so far.

Metronomic cyclophosphamide enhances HPV16E7 peptide vaccine induced antigen-specific and cytotoxic T-cell mediated antitumor immune response

“…32,41 To compensate, low dose CPA treatment has been combined with drugs that specifically reduce MDSC levels such as gemcitabine or ATRA. [42][43][44] We found that the combination of mCPA plus DPX-R9F did not increase MDSC levels, negating the need for additional drugs. MDSC's are essentially akin to haematopoietic stem/ progenitor cells arrested in development, presumably by the inflammatory cytokine milieu created by the tumor.…”

Therapeutic regulation of myeloid-derived suppressor cells and immune response to cancer vaccine in patients with extensive stage small cell lung cancer

“…ATRA also has been shown to improve the differentiation of DC in cancer patients [38] and to drive the differentiation of monocytes into DC-like cells [39]. Treatment of tumor-bearing mice with ATRA substantially decreased the number of MDSC in spleens and enhanced the effect of cancer vaccines [21, 24–26]. Treatment of patients with renal cell carcinoma showed a substantial reduction in the level of MDSC in peripheral blood [27].…”

“…In previous studies ATRA showed a direct effect on MDSC by causing apoptosis of PMN-MDSC and differentiating M-MDSC to mature myeloid cells (macrophages and DC) [21–23]. Treatment of tumor-bearing mice with ATRA substantially decreased the presence of MDSC in spleens [21, 24–26]. Treatment of patients with renal cell carcinoma showed a substantial reduction in the level of MDSC in peripheral blood [27].…”

Therapeutic vaccination against human papilloma virus induced malignancies

“…Specifically, large tumors could be treated with intense regimens in which cyclophosphamide was followed by vaccination in combination with all trans retinoic acid. The latter is known to reduce MDSC and to improve immunity but also to increase Tregs [51], the effect of which probably was prevented by cyclophosphamide pretreatment as this tritherapy locally reduced MDSC, Tregs, and the secretion of immunosuppressive cytokines [52 ]. Other non-mutually exclusive measures are COX-2 inhibitors or TGFb type I receptor kinase inhibitors that both mediate the generation of a Th1 type of microenvironment resulting in increased local immune cell trafficking allowing vaccines to effectively eradicate large tumors [53,54].…”