Abstract PS17-20: Response to a modified whole tumor cell targeted immunotherapy in patients with advanced breast cancer correlates with tumor grade

Abstract Background: SV-BR-1-GM is a GM-CSF transfected breast cancer cell line, exceptional for having antigen-presenting capability and expressing both HLA I and II. The parent cell line, SV-BR-1, was derived from a patient with grade II (moderately differentiated) breast cancer. We report molecular characterization of SV-BR-1-GM, noting it retains features of a grade II tumor, and report enhanced disease control in patients with grade I or II breast cancer.Methods: SV-BR-1 and SV-BR-1-GM were characterized molecularly using RNAseq and proteomic analyses. We treated 23 evaluable patients with recurrent and/or metastatic breast cancer refractory to standard therapy. The SV-BR-1-GM regimen included cyclophosphamide 300 mg/m2 2-3d prior to intradermal injection of SV-BR-1-GM (20-40x106 cells divided into 4 sites) and IFNα into the inoculation sites (10,000 IU/site) about 48 and 96 hours subsequently. Cycles were q2 weeks x3 then qmo x 3 (clinical trial NCT03066947). Eleven patients were treated with the above regimen in combination with a PD-1 inhibitor (pembrolizumab or INCMGA00012) (clinical trial NCT03328026). Disease response was evaluated radiographically q3 mo and as clinically indicated. Results: To estimate the tumor grade represented by the SV-BR-1-GM cell line, we developed a score we refer to as Relative Molecular Grade (RMG). SV-BR-1-GM is most similar to the MDA-MB-468 cell line (RMG of 52.1), which was classified as Basal A phenotype. Basal A cancers are less aggressive than Basal B but more aggressive than Luminal, suggesting that SV-BR-1-GM may have retained features of a grade II breast cancer. We also noted that SV-BR-1-GM expresses both Class I (HLA-A, B & C) and Class II (HLA-DR and -DP) molecules, and that the HLA-DR expression is enhanced by treatment with IFNγ. SV-BR-1-GM expressed 31 genes which are overexpressed in breast cancer, 8 cancer-testis antigens and 3 genes expressed in breast tissue. In 30 patients treated with the SV-BR-1-GM regimen (19 with the SV-BR-1-GM regimen alone, 4 who began on the SV-BR-1-GM regimen and transitioned to combination with a PD-1i, and 7 with combination therapy alone) there were 7 with grade II breast cancer and 1 with grade I breast cancer (Table). These patients were heavily pre-treated with an average of 10 prior regimens. While only one patient with grade III cancer showed disease control, 75% of the patients with grade I or II tumors showed disease control. Patients remained on study for up to 259 days.Conclusions: SV-BR-1-GM appears to retain characteristics of a moderately differentiated breast cancer, expresses multiple potential tumor antigens, and can elicit disease control especially in patients with grade I and II breast cancer. TablePatients with Grade I/II TumorsCharacteristicSV-BR-1-GM Regimen Alone(n=6)SV-BR-1-GM Regimen + PD-1i(n=3)All Patients(n=8)Age64 ± 767 ± 465 ± 7Mean Prior Systemic Regimens6 (range 1-20)15 (range 14-15)10 (range 1-20)% ER/PR +80%100%86%% Her2/neu +0%33%14%% Triple Negative20%0%14%Delayed-type Hypersensitivity83%100%88%Disease Control Rate*67%100%75%Days on Study (Range)94 (32-181)189 (133-259)141 (32-259)•Includes CR, PR, SD (including minor responses and mixed responses) Citation Format: William Williams, Shaker R Dakhil, Carmen Calfa, Jarrod P Holmes, Saveri Bhattacharya, Jason Lukas, Elizabeth Tan-Chiu, George E Peoples, Vivek G Sunkari, Markus D Lacher, Charles L Wiseman. Response to a modified whole tumor cell targeted immunotherapy in patients with advanced breast cancer correlates with tumor grade [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS17-20

Abstract P2-14-02: Overall survival following treatment with a modified whole tumor cell targeted immunotherapy in patients with advanced breast cancer

Abstract Background: SV-BR-1-GM is a GM-CSF secreting breast cancer cell line derived from a Grade II (moderately differentiated) breast tumor that also expresses HLA class I & II antigens and is able to function as an antigen-presenting cell. Irradiated SV-BR-1-GM is used in a regimen including pre-dose low-dose cyclophosphamide and post-dose injection of IFNα2b into the inoculation sites. The SV-BR-1-GM regimen has been used alone (“monotherapy”, ClinicalTrials.gov NCT03066947 - study completed) and in combination with checkpoint inhibitors (“combination”, ClinicalTrials.gov NCT03328026 - study ongoing). Here we report survival data for patients with advanced metastatic breast cancer (aMBC) treated with the SV-BR-1-GM regimen. Methods: 27 patients with refractory aMBC were treated with the SV-BR-1-GM regimen as monotherapy (cycles every 2 weeks x3 and then monthly). The combination study uses the SV-BR-1-GM regimen with PD-1 inhibitors (PD-1i) pembrolizumab or retifanlimab with cycles every 3 weeks (12 patients dosed to date). Here we report progression free survival (PFS) and overall survival (OS) for patients where that data was collected. Results: A total of 35 patients received the SV-BR-1-GM regimen. The SV-BR-1-GM regimen alone (monotherapy) was given to 27 and 12 received the regimen with a PD-1i checkpoint inhibitor (combination therapy): 4 subjects crossed over from monotherapy. Patients had been heavily pre-treated, median prior regimens = 5. Most patients were estrogen receptor and/or progesterone receptor positive, 18% were Her2/neu positive and 33% were triple negative. The treatment was generally safe and well tolerated. The disease control rate was 30% for the SV-BR-1-GM regimen alone and 33% for the combination with a PD-1i. Several patients had objective complete regression of selected metastases. Median progression free survival was 2.8 months for the SV-BR-1-GM regimen alone and 4.2 months for the PD-1i combination. Median overall survival was 7.0 months for the SV-BR-1-GM regimen alone (data available on 9 patients), and 12.0 months for the PD-1i combination (data available on 7 patients). Conclusions: The median OS compares favorably with published data regarding survival in third line trials (Kazmi Breast Cancer Res Treat. 2020 Aug 17). The protracted OS seen in some subjects suggests some patient subpopulations are more likely to derive clinical benefit. The SV-BR-1-GM regimen alone or in combination with a PD-1i, when administered to heavily pre-treated patients with aMBC, may have elicited effective immune responses in some patients. TablePatients by StudyCharacteristicSV-BR-1-GM Regimen Alone (n=27)SV-BR-1-GM Regimen + PD-1i (n=12)All Patients* (n=35)Age60 ± 1063 ± 1060 ± 10Mean Prior Systemic Regimens5 (range 0-12)6 (range 1-10)5 (range 0-12)% ER/PR +52%75%58%% Her2/neu +15%17%18%% Triple Negative36%25%33%Delayed-type Hypersensitivity81%91%82%Disease Control Rate30%33%29%Median (Range) Progression Free Survival (months)2.8 (0.4-7.4) (n=27)4.2 (0.8-9.4) (n=11)2.8 (0.4-9.4) (n=34)Median (Range) Overall Survival (months)7.0 (1-41) (n=9)12.0 (5.1-21.4) (n=7)10.2 (1-41) (n=14)• Note that 4 patients crossed over from the monotherapy study to the combination therapy study. Citation Format: William Williams, Shaker R Dakhil, Carmen Calfa, Jarrod P Holmes, Saveri Bhattacharya, Jason Lukas, Elizabeth Tan-Chui, George E Peoples, Vivek G Sunkari, Markus D Lacher, Charles L Wiseman. Overall survival following treatment with a modified whole tumor cell targeted immunotherapy in patients with advanced breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P2-14-02

Abstract P3-09-08: Efficacy and safety of a modified whole tumor cell targeted immunotherapy in patients with advanced breast cancer alone and in combination with immune checkpoint inhibitors

Abstract Background: SV-BR-1-GM is a GM-CSF transfected breast cancer cell line, exceptional for having antigen-presenting capability expressing both HLA I and II. We report clinical efficacy, safety, and immunologic correlates of response from our initial Phase I/II trial and initial data from our trial of SV-BR1-GM in combination with immune checkpoint inhibitors. Methods: We enrolled patients with recurrent and/or metastatic breast cancer refractory to standard therapy. Patients received cyclophosphamide 300 mg/m2 2-3d prior to intradermal injection of SV-BR-1-GM (20-40 × 106 cells divided into 4 sites) and IFNα into the inoculation sites (10,000 IU/site) ~2 & 4 days subsequently. Cycles were q2 weeks x3 then qmo x 3. Adverse events (AE) were evaluated after each inoculation. Immunologic responses were measured by delayed type hypersensitivity (DTH) after each inoculation with humoral and cellular responses evaluated ~q3 mo. Disease response was evaluated radiographically q3 mo and as clinically indicated (clinical trial NCT03066947). A similar regimen was used with SV-BR-1-GM in combination with pembrolizumab (200 mg IV) with cycles every 3 weeks (Phase I/II study NCT03328026). Results: In Phase I/IIa (NCT03066947), 23 patients underwent 1 - 8 cycles of treatment. Tumor regression was seen in 3 patients, all of whom matched SV-BR-1-GM at least at one HLA allele. There were no related serious adverse events. The most common adverse event was minor local irritation at the inoculation site. Clinical data are shown in the table. A measurable DTH response was present in 21 patients. Of patients who developed a DTH response and had at least one HLA match, the tumor regression rate was 33% and for those with 2 HLA matches 67%. We saw evidence of antibody responses in 3 of 5 patients evaluated to date. Especially in responders after treatment, blood lymphocytes showed increased cytokine secretion (including ITAC, IFNγ, IL-6 & IL-8) following stimulation with antigens expressed in SV-BR-1-GM. 21/23 patients had expression of PD-L1 in identified circulating cancer-associated cells, and expression levels increased with treatment. Therefore, a combination study with pembrolizumab was initiated. Data on the first 6 patients shows that the regimen is clinically active and safe. One patient with a robust DTH response had evidence of tumor regression in liver metastases. This study is ongoing and is being modified to evaluate combination therapy with the PD-1 inhibitor INCMGA00012 and the IDO inhibitor epacadostat. Conclusions: SV-BR-1-GM appears to be safe and well-tolerated. Contrary to conventional wisdom, SV-BR-1-GM can produce regression of metastatic breast cancer correlating with an immunologic response and HLA matching. Combination therapy with checkpoint inhibitors is ongoing. Citation Format: William Williams, Shaker R Dakhil, Jarrod P Holmes, Saveri Bhattacharya, Carmen Calfa, Ajay Kundra, Daniel L Adams, Diane DaSilva, George E Peoples, Vivek Sunkari, Markus Lacher, Charles L Wiseman. Efficacy and safety of a modified whole tumor cell targeted immunotherapy in patients with advanced breast cancer alone and in combination with immune checkpoint inhibitors [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P3-09-08