Cancer Antigen Discovery Program

Characterization of the Human Immune Response

Careful and systematic monitoring of the response to vaccination is the only way to measure the success or failure of immunization, and allow for the optimization of the treatment strategy. Meaningful evaluation, to determine safety and induction of specific immunity, of a cancer vaccine for humans is only possible in a human setting.

Introduction

Meticulous immune monitoring of patients receiving a cancer vaccine, in order to evaluate vaccine-induced immune responses, is a central tenet of LICR cancer vaccine development. In the LICR Clinical Trials Program, single trial variables of vaccine development and optimization are tested in multiple parallel studies at several clinical centers. To enable data from these parallel studies to be meaningfully compared, LICR has developed standardized immune monitoring methodologies for measuring humoral (antibody) and cellular (CD8+ and CD4+ T cell) immune responses. Much of the knowledge required to develop these methodologies was obtained through painstaking and detailed analyses of cases of spontaneous immunity. To ensure that cancer vaccines are given to appropriate clinical trial candidates, those whose tumors express appropriate antigens and HLA types, standardized molecular and immunohistochemical typing methods have also been adopted to evaluate patients before trial entry (see Cancer Antigen Characterization).

Immunological monitoring of immunized patients, as described briefly below, has shown that patients receiving LICR therapeutic cancer vaccines are being successfully immunized against cancer antigens. Phase II clinical trials (Cancer Vaccines), and further development of these vaccines (Vaccine Composition) to assess and enhance clinical efficacy are ongoing.

Serological Assessment

LICR investigators are using standardized enzyme-linked immunosorbent assays (ELISA), as well as western blot methodologies and reagents to monitor for the presence of antigen-specific antibodies in the serum of vaccinated patients. Detecting the generation of antigen-specific antibodies generation is essential, as it is likely that the most efficacious therapeutic cancer vaccines will induce an integrated (antibody plus CD8+ and CD4+ T cell) immune response. Thus the ability of a vaccine to induce antigen-specific antibodies is a key factor in monitoring the immune response to a vaccine, and in the optimization of Vaccine Compositions.

T cell Responses

In clinical evaluations, LICR investigators employ either peptide or protein antigen to assess the patient’s delayed type hypersensitivity (DTH) reaction. This procedure is used routinely for allergy testing, and is a minimally-invasive and simple assessment for the presence of antigen-specific T cells in patients before (for spontaneous immunity) and following (for evidence of immunization) vaccination.

For more sensitive and quantitative monitoring, LICR investigators have developed several standardized methods for measuring T cells specific for defined antigen peptides. Fluorescent-labeled tetrameric HLA-peptide complexes (‘Tetramers’) provide a quantification of specific CD8+ T cells, and are generated in the LICR’s central Tetramer Facility (Lausanne, Switzerland). Complementary tetramer reagents for measuring CD4+ T cells are currently being developed. Additionally, ‘ELISPOT’ assays that measure the T cell-induced release of cytokines following stimulation with specific peptide(s) are used to quantify functional, antigen-specific CD8+ and CD4+ T cells.

Novel methodologies for the complete evaluation of broad antigen-specific responses induced by full-length protein antigens are now being developed and optimized. One such method is to isolate antigen presenting cells (APCs) from a blood sample from the patient (‘autologous’ APCs), and use these together with the full-length, or near full-length, antigen to detect and measure antigen-specific CD8+ and CD4+ T cells.

Another method being developed for immunological monitoring combines the selective stimulation and expansion (in number) in vitro of antigen-specific T cells with limiting dilution analysis. This enables the clonal analysis of the emergence and evolution of discrete, vaccine-induced T cell specificities. Additionally, to eliminate any theoretical bias that in vitro expansion may introduce, complementary immune monitoring methods are being adapted for the direct ex vivo assessment (from a patient’s blood sample) of antigen-specific T cells. The establishment of such methods would enable additional phenotypic characterization of the vaccine-induced antigen-specific T cells.

Key Publications