Because patients and their tumors are so variable, one should include a mix of memory antigens (usually protein for CD4+ recall responses 30) to evaluate immune competence and changes throughout vaccination. This will also help to more objectively categorize an immune response as “strong” or “weak,” e.g. by comparing a vaccine-specific CTL response to an endogenous CMV response
if class I control peptides also are used. In addition, it is my personal opinion that we should also load a separate batch of control DC with relevant antigens for priming (e.g. HIV or other viral epitopes) to identify a superior DC vaccine in a small number of RXDX-106 patients. With increased vaccine efficacy, T cells will become more often detectable ex vivo, so that one can also sort tetramer-positive T cells for easier testing of mono- versus polyclonality
(the latter observed to occur with cocktail-matured DC 71, 72), polyfunctionality (which correlates – at least in viral disease – with clinical benefit 73, proliferative capacity (relevant as it reflects one memory T-cell feature), and transcriptome analysis (which appears to reflect priming by different vaccines, and in case of DC vaccines might reflect the DC transcriptome 74). With enhanced DC vaccines, one should then even see characteristic cellular and/or humoral signatures in whole blood as observed in case of the strong yellow fever vaccine Fluorouracil 75–78. Immunomonitoring requires standardization and reproducibility, ALOX15 an important component of which are discussion groups (e.g. the MIATA project, www.miataproject.org) and proficiency panels, which are already offered for tetramer staining, intracellular cytokine labeling, and Elispot assays by the CVC and the CIMT (see www.cancerresearch.org
and www.cimt.eu, respectively). I strongly support participation in such intercomparison programs to facilitate accurate and transparent data presentation. These are also high on the list of priorities, as MoDC cultured in GM-CSF+IL-15 are superior in vitro in inducing high-affinity CTL 79, 80. It remains difficult for us to generate a sufficient number of highly standardized DC under these conditions, which is a prerequisite for true GMP production. I suspect that similar problems have occurred to others, which explains why there are no data available yet on their immunogenicity in vivo in humans. First reported by E. Gilboa in 1996 (for review see 81), RNA-transfection of DC offers distinct opportunities, particularly since the unreliable “simple” addition of mRNA to DC has been substituted by electroporation 82, which allows strong protein expression and intracellular staining in the majority of DC, a prerequisite for reproducibility, validation, and thus GMP production 83. A crucial regulatory advantage is that mRNA transfection does not constitute gene therapy as mRNA is not integrated into the genome.