T cell costimulation has great therapeutic potential if it can be optimized and controlled. To achieve this, we engineered T cell-activating fusion
proteins and immunocytokines that specifically attach to
viral antigens of a virus-infected
tumor vaccine. We employed the avian Newcastle Disease Virus because this agent is highly efficient for human
tumor cell
infection, and leads to introduction of
viral hemagglutinin-
neuraminidase (HN) molecules at the
tumor cell surface. Here, we demonstrated the strong potentiation of the T cell stimulatory activity of such a
vaccine upon attachment of bispecific or trispecific fusion
proteins which bind with one arm to viral HN molecules of the
vaccine, and with the other arm either to CD3 (signal 1), to CD28 (costimulatory signal 2a), or to
interleukin-2 receptor (costimulatory signal 2b) on T cells. A
vaccine with a combination of all three signals triggered the strongest activation of naïve human T cells, thereby inducing the most durable bystander antitumor activity in vitro. Adoptive transfer of such polyclonally activated cells into immunodeficient mice bearing human
breast carcinoma caused
tumor regression. Furthermore,
tumor-reactive memory T cells from draining lymph nodes of
carcinoma patients could be efficiently reactivated in a short-term ELISpot assay using an autologous
tumor vaccine with optimized signals 1 and 2, but not with a similarly modified
vaccine from an unrelated tumor cell line. Our data describe new bioactive molecules which in combination with an established virus-modified
tumor vaccine greatly augments the antitumor activity of T cells from healthy donors and
cancer patients.