Regulatory T (T(reg)) cells mediate homeostatic peripheral tolerance by suppressing autoreactive T cells. Failure of host antitumor immunity may be caused by exaggerated suppression of tumor-associated antigen-reactive lymphocytes mediated by T(reg) cells; however, definitive evidence that T(reg) cells have an immunopathological role in human cancer is lacking. Here we show, in detailed studies of CD4(+)CD25(+)FOXP3(+) T(reg) cells in 104 individuals affected with ovarian carcinoma, that human tumor T(reg) cells suppress tumor-specific T cell immunity and contribute to growth of human tumors in vivo. We also show that tumor T(reg) cells are associated with a high death hazard and reduced survival. Human T(reg) cells preferentially move to and accumulate in tumors and ascites, but rarely enter draining lymph nodes in later cancer stages. Tumor cells and microenvironmental macrophages produce the chemokine CCL22, which mediates trafficking of T(reg) cells to the tumor. This specific recruitment of T(reg) cells represents a mechanism by which tumors may foster immune privilege. Thus, blocking T(reg) cell migration or function may help to defeat human cancer.

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Tumor infiltrating lymphocytes (TIL) play an essential role in mediating response to chemotherapy and improving clinical outcomes in all subtypes of breast cancer. Triple negative breast cancers (TN) are most likely to have tumors with >50 % lymphocytic infiltrate, termed lymphocyte predominant breast cancer, and derive the greatest survival benefit from each 10 % increase in TIL. The majority of HER2+ breast cancers have similar level of immune infiltrate as TN breast cancer yet the presence of TILs has not shown the same survival benefit. For HER2+ breast cancers, type 1 T-cells, either increased TBET+ tumor infiltration or increased type 1 HER2-specific CD4+ T-cells in the peripheral blood, are associated with better outcomes. Hormone receptor positive HER2 negative tumors tend to have the least immune infiltrate yet are the only breast cancer subtype to show worse prognosis with increased FOXP3 regulatory T-cell infiltrate. Notably, all breast cancer subtypes have tumors with low, intermediate, or high TIL infiltrate. Tumors with high TILs may also have increased PD-L1 expression which might be the reason that TN breast cancer seems to demonstrate the most robust clinical response to immune checkpoint inhibitor therapy but further investigation is needed. Tumors with intermediate or low levels of pre-treatment immune infiltrate, on the other hand, may benefit from an intervention that may increase TIL, particularly type 1 T-cells. Examples of these interventions include specific types of cytotoxic chemotherapy, radiation, or vaccine therapy. Therefore, the systematic evaluation of TIL and specific populations of TIL may be able to both guide prognosis and the appropriate sequencing of therapies in breast cancer.

Historically, cancer-directed immune-based therapies have focused on eliciting a cytotoxic T cell (CTL) response, primarily due to the fact that CTL can directly kill tumors. In addition, many putative tumor antigens are intracellular proteins, and CTL respond to peptides presented in the context of MHC class I which are most often derived from intracellular proteins. Recently, increasing importance is being given to the stimulation of a CD4+ T helper cell (Th) response in cancer immunotherapy. Th cells are central to the development of an immune response by activating antigen-specific effector cells and recruiting cells of the innate immune system such as macrophages and mast cells. Two predominant Th cell subtypes exist, Th1 and Th2. Th1 cells, characterized by secretion of IFN-gamma and TNF-alpha, are primarily responsible for activating and regulating the development and persistence of CTL. In addition, Th1 cells activate antigen-presenting cells (APC) and induce limited production of the type of antibodies that can enhance the uptake of infected cells or tumor cells into APC. Th2 cells favor a predominantly humoral response. Particularly important during Th differentiation is the cytokine environment at the site of antigen deposition or in the local lymph node. Th1 commitment relies on the local production of IL-12, and Th2 development is promoted by IL-4 in the absence of IL-12. Specifically modulating the Th1 cell response against a tumor antigen may lead to effective immune-based therapies. Th1 cells are already widely implicated in the tissue-specific destruction that occurs during the pathogenesis of autoimmune diseases, such as diabetes mellitus and multiple sclerosis. Th1 cells directly kill tumor cells via release of cytokines that activate death receptors on the tumor cell surface. We now know that cross-priming of the tumor-specific response by potent APC is a major mechanism of the developing endogenous immune response; therefore, even intracellular proteins can be presented in the context of MHC class II. Indeed, recent studies demonstrate the importance of cross-priming in eliciting CTL. Many vaccine strategies aim to stimulate the Th response specific for a tumor antigen. Early clinical trials have shown that focus on the Th effector arm of the immune system can result in significant levels of both antigen-specific Th cells and CTL, the generation of long lasting immunity, and a Th1 phenotype resulting in the development of epitope spreading.

The toxicities of immunotherapy for cancer are as diverse as the type of treatments that have been devised. These range from cytokine therapies that induce capillary leakage to vaccines associated with low levels of autoimmunity to cell therapies that can induce damaging cross-reactivity with normal tissue to checkpoint protein inhibitors that induce immune-related adverse events that are autoinflammatory in nature. The thread that ties these toxicities together is their mechanism-based immune nature and the T-cell–mediated adverse events seen. The basis for the majority of these adverse events is a hyperactivated T-cell response with reactivity directed against normal tissue, resulting in the generation of high levels of CD4 T-helper cell cytokines or increased migration of cytolytic CD8 T cells within normal tissues. The T-cell immune response is not tissue specific and may reflect a diffuse expansion of the T-cell repertoire that induces cross-reactivity with normal tissue, effectively breaking tolerance that is active with cytokines, vaccines, and checkpoint protein inhibitors and passive in the case of adoptive cell therapy. Cytokines seem to generate diffuse and nonspecific T-cell reactivity, whereas checkpoint protein inhibition, vaccines, and adoptive cell therapy seem to activate more specific T cells that interact directly with normal tissues, potentially causing specific organ damage. In this review, we summarize the toxicities that are unique to immunotherapies, emphasizing the need to familiarize the oncology practitioner with the spectrum of adverse events seen with newly approved and emerging modalities.

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Immunomodulatory strategies, such as antibody therapy and cancer vaccines, are increasingly being considered as potential adjuvant therapies in patients with advanced stage breast cancer to either treat minimal residual disease or prevent relapse. However, little is known concerning the incidence and magnitude of the pre-existent breast cancer specific immune response in this patient population. Using the HER-2/neu oncogenic protein as a model, a well-defined tumor antigen in breast cancer, we questioned whether patients with advanced stage HER-2/neu overexpressing breast and ovarian cancers (III/IV) had evidence of pre-existent immunity to HER-2/neu. Forty-five patients with stage III or IV HER-2/neu overexpressing breast or ovarian cancer were evaluated for HER-2/neu specific T cell and antibody immunity. Patients enrolled had not received immunosuppressive chemotherapy for at least 30 days (median 5 months, range 1-75 months). All patients were documented to be immune competent prior to entry by DTH testing using a skin test anergy battery. Five of 45 patients (11%) were found to have a significant HER-2/neu specific T cell response as defined by a stimulation index > or = 2.0 (range 2.0-7.9). None of eight patients who were HLA-A2 had a detectable IFNgamma secreting T-cell precursor frequency to a well-defined HER-2/neu HLA-A2 T cell epitope, p369-377. Three of 45 patients (7%) had detectable HER-2/neu specific IgG antibodies, range 1.2-8.9 microg/ml. These findings suggest that patients with advanced stage HER-2/neu overexpressing breast and ovarian cancer can mount a T cell and/or antibody immune response to their tumor. However, in the case of the HER-2/neu antigen, the pre-existent tumor specific immune response is found only in a minority of patients.

Purpose: The HER-2/neu protein is a nonmutated tumor antigen that is overexpressed in a variety of human malignancies, including breast and ovarian cancer. Many tumor antigens, such as MAGE and gp100, are self-proteins; therefore, effective vaccine strategies must circumvent tolerance. We hypothesized that immunizing patients with subdominant peptide epitopes derived from HER-2/neu, using an adjuvant known to recruit professional antigen-presenting cells, granulocyte-macrophage colony-stimulating factor, would result in the generation of T-cell immunity specific for the HER-2/neu protein.Patients and Methods: Sixty-four patients with HER-2/neu-overexpressing breast, ovarian, or non-smallcell lung cancers were enrolled. Vaccines were composed of peptides derived from potential T-helper epitopes of the HER-2/neu protein admixed with granulocyte-macrophage colony-stimulating factor and administered intradermally. Peripheral-blood mononuclear cells were evaluated at baseline, before vaccination, and after vaccination for antigen-specific T-cell immunity.Immunologic response data are presented on the 38 subjects who completed six vaccinations. Toxicity data are presented on all 64 patients enrolled.Results: Ninety-two percent of patients developed T-cell immunity to HER-2/neu peptides (stimulation index, 2.1 to 59) and 68% to a HER-2/neu protein domain (stimulation index range, 2 to 31). Epitope spreading was observed in 84% of patients and significantly correlated with the generation of a HER-2/neu protein-specific T-cell immunity (P ‫؍‬ .03). At 1-year follow-up, immunity to the HER-2/neu protein persisted in 38% of patients. Conclusion:The majority of patients with HER-2/ neu-overexpressing cancers can develop immunity to both HER-2/neu peptides and protein. In addition, the generation of protein-specific immunity, after peptide immunization, was associated with epitope spreading, reflecting the initiation of an endogenous immune response. Finally, immunity can persist after active immunizations have ended.