Breaking B‐cell Tolerance and CTL Tolerance in three OVA‐transgenic Mouse Strains Expressing Different Levels of OVA

It is of major importance to overcome the immunological tolerance in attempts to generate efficient tumour vaccines. Here, we describe induction of autoantibodies and self-reactive CTL in three types of OVA-transgenic mouse strains, RIP-OVAlow, RIP-mOVA and RIP-OVAHI exhibiting varying levels of OVA expression and tolerance. This was achieved by immunizing with DNA constructs where a foreign T-helper epitope, P30 from tetanus toxin, was inserted into the OVA sequence. OVA wild-type DNA as well as the P30-modified OVA DNA vaccines (OVA-P30) were constructed and used for immunization in the OVA-transgenic mouse strains as well as in control C57Bl/6 mice. The data show that insertion of a foreign T-helper peptide (P30) in OVA is sufficient for breaking B-cell tolerance in three different OVA-transgenic mice strain. This approach is sufficient for induction of self-reactive CTL in two of the three strains that expressed either a membrane-bound form of OVA or a low amount of soluble OVA. It was not possible to induce CTL but still possible to induce autoantibodies in the strain that expressed a higher level of soluble OVA.