Enhanced Anti-Breast Cancer Cytotoxicity after Autologous Peripheral Blood Stem Cell Transplant (PBSCT) by Boosting with Multiple Infusions of Activated T Cells (ATC) Armed with Anti-CD3 x Anti-Her2 Bispecific Antibody (Her2Bi) Prior to PBSCT.

More aggressive treatment strategies are needed for women with metastatic breast cancer(mBrCa). Although peripheral blood stem cell transplant (PBSCT) permits the use of high-dose chemotherapy (HDC) that could not otherwise be given, results for PBSCT have not been encouraging. In order to boost tumor kill, we combined a protocol that targets Her2 using activated T cells (ATC) armed with anti-CD3 × anti-Her2 bispecific antibody (Her2Bi) with a second protocol that involves infusions of ATC after PBSCT to boost anti-tumor immunity. In our phase I trial using ATC with Her2Bi to treat women with mBrCA who have Her2 positve or negative disease, we found that multiple infusions of armed ATC induced cytotoxicity directed at BrCa cells in the peripheral blood mononuclear cells (PBMC) of the patients that develop in 2 weeks and last up to 4 mos (Clin Canc Res12:569,2006). Armed ATC lyse tumors that are Her2 low-expressors (0–1+). Targeting leads to specific cytotoxicity, induces cytokine/chemokine release, and proliferation of the armed ATC. In a second study, ATC were infused after PBSCT into 23 women with mBrCa leading to 70% overall survival and 50% progression free survival at 32 mos after PBSCT. Therefore, the combined strategy involved obtaining T cells by another leukopheresis after the boosting with armed ATC, expanding the immune T cells and infusing the expanded ATC after PBSCT to transfer pre-immune anti-BrCa cytotoxicity to reconstitute cytotoxicity after PBSCT. Two patients (one pt was Her2 3+ ; one pt was Her2 0–1+) underwent treatment with this treatment approach. Both patients were given 8 infusions (20 billion/infusion with a total of 160 billion) of ATC armed with Her2Bi in the first protocol and subsequently leukopheresed and ATC were produced for the second protocol. The expanded ATC at an effector:target ratio (E/T) of 25:1, exhibited cytotoxicity at BrCa tumor cells (SK-BR-3) at 71% and 75% for pts 1 and 2, respectively. The cell product for pt 1 contained 68% CD3+, 32% CD4+, 39% CD8+, 29% CD16+56+, 12% CD4+CD25+, and 15% CD8+CD25+ cells and the cell product for pt 2 contained 35% CD3+, 25% CD4+, 8.5% CD8+, 23.3% CD16+56+, 10.4% CD4+CD25+, and 4.7% CD8+CD25+ cells. The protocol involves infusing 15 doses of ATC after PBSCT with 3 doses of ATC/week for 3 weeks and then ATC once/week for six more weeks. The pt1 and pt 2 received total of 114 and 70 billion ATC, respectively. Pt1 developed anti-BrCA cytotoxicity of 9% 2 weeks after PBSCT. Pt2 exhibited anti-BrCa cytotoxicity at an E:T of 25:1 of 38% and 15% at 3 weeks and 6 months after PBSCT, respectively. Phenotyping of peripheral blood at 6 mos after PBSCT showed 61% CD3+, 36% CD4+, 19.5% CD8+, and 15.5% CD56+ cells. There was no cytotoxicity directed at Daudi cells. These data strongly suggest that transfer of pre-immune cells after PBSCT accelerate immune reconstitution of tumor specific cytotoxicity after PBSCT. The preboost strategy with targeted T cells is being combined in a proof of principle trial to assess whether enhanced cytotoxicity can be consistently enhanced after PBSCT.