Abstract P3-05-16: A mathematical model for predicting immune response in a trastuzumab treated HER2+ breast cancer animal model: Preliminary efforts

Introduction: Trastuzumab is a targeted antibody to the human epidermal growth factor receptor 2 (HER2) that induces cell cycle arrest and is used in the treatment of HER2+ positive breast cancer. We have recently presented in vivo evidence in a murine model that trastuzumab also improves vascular delivery of subsequent cytotoxic therapies. The mechanism by which trastuzumab and the immune system interact to regulate tumor-associated angiogenesis is not well characterized. Therefore, we offer a preliminary report on a mathematical framework to systematically investigate the potential interactions among the immune response, tumor cells, vasculature, and other environmental factors based on experimental data for the BT474 murine model of HER2+ breast cancer.

Experimental: BT474 breast cancer cells were implanted subcutaneously into athymic nude mice. After tumors reached 250 mm3, mice were treated with trastuzumab or saline, tumor volumes were recorded, and tumors were extracted at various times over seven days. Immunohistochemistry for treated and control tumors were evaluated for 0, 1, 3, 4, and 7 days post trastuzumab treatment. Histology data includes: percent hypoxia (pimonidazole), percent necrosis, and vascular maturation index (VMI, ratio of alpha-smooth muscle actin to total vessel counts as stained with CD31). Ongoing studies are quantifying immune cell infiltration through immunofluorescent imaging of F4/80 and CD11c expression.

Modeling: We developed a system of five coupled, ordinary differential equations that accounts for the temporal variation in tumor growth, vasculature, hypoxia, necrosis, and immune response. The general immune response component corresponds to the mouse's pro-inflammatory responses, as T cell driven responses are absent in this murine model. Uncertainty analysis was performed to verify plausible overlap between the model's predictions and the experimental data—where local and global samplings of all parameters were used to generate potential model results to be compared to the data for both control and treated mouse sets. Sensitivity analysis was performed using Sobol' Indices to determine the driving parameters of the system to identify target parameters for experimental estimation. The model parameters were calibrated using mean and standard deviations for the available data (tumor volume, VMI, percentage of hypoxia, and percentage of necrosis) for each experimental time point to predict the differences of the immune component between the treated and control tumors.

Results and Discussion: The model is well behaved and can be calibrated with the available data. The model predicts distinct differences for the immune response between the control and treated groups—showing increasing versus decreasing immune component values over time for treated versus control results, respectively. Preliminary results from the immunofluorescent imaging data support the immunological predictions of the model; in particular, the amount of immune infiltration (i.e., more immune cells) in necrotic areas is greater in the treated than the untreated tumors (p<0.025).

We acknowledge the support of CPRIT RR160005 and NCI R01CA186193.

Citation Format: Jarrett AM, Yankeelov TE, Ehrlich LI, Godfrey W, Sorace AG. A mathematical model for predicting immune response in a trastuzumab treated HER2+ breast cancer animal model: Preliminary efforts [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-05-16.

Overall survival (OS) analysis of a phase II randomized controlled trial (RCT) of a poxviral-based PSA targeted immunotherapy in metastatic castration-resistant prostate cancer (mCRPC)

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Background: Therapeutic poxviral vaccines for prostate cancer are safe with preliminary evidence of clinical benefit in phase I/II studies. PROSTVAC-VF (PV) comprises 2 recombinant viral vectors (Vaccinia and Fowlpox), each encoding transgenes for prostate specific antigen (PSA) and 3 immune costimulatory molecules (B7.1, ICAM-1, and LFA3: TRICOM). PV is administered subcutaneously in a heterologous prime-boost regimen with concurrent low-dose GM-CSF. Methods: 122 patients (pts) were treated in a multi-center, double-blind, RCT of a vaccination series. Pts were randomized 2:1 to PV + GM-CSF vs. placebo empty vector + control saline injections (C). Vaccinia-based vector was used for priming followed by 6 planned Fowlpox-based vector boosts. The trial completed enrollment in July 2005. Eligible pts had metastatic disease, a rising PSA despite castrate testosterone levels, and a Gleason score of ≤7. Pts with a history of prior chemotherapy use, visceral metastasis, or narcotic use were excluded. The 1º endpoint was progression free survival (PFS), with progression defined as 2 new lesions on bone scan or RECIST-defined progression. Vaccination was discontinued after progression. Results: 82 pts received PV and 40 received C. Pt characteristics were similar (means): age (72PV/76C), PSA (134PV/188C), Alk-Phos (142PV/159C), LDH (207PV/218C), Hgb (13PV/13C), and number bone metastatic sites (5.3PV/6.5C). Mean number of vaccinations was 5.4 PV and 5.3 C. PFS was similar in the 2 groups (p = 0.56). However, at 3 years post study, PV patients had a better overall survival than C patients (25 alive, 30%, PV, versus 7 alive, 17%, C) and a longer median survival (24.5 months PV, versus 16 months C); estimated hazard ratio 0.6 (95% CI 0.4–0.9); stratified log rank p = 0.016. Conclusions: In a RCT, PV immunotherapy was associated with an 8.5 month improvement in median OS in men with mCRPC. These data provide evidence of prolonged anti-tumor activity, but need to be confirmed in a larger phase III study.

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A novel five-transmembrane hematopoietic stem cell antigen: isolation, characterization, and molecular cloning

Phenotypic analysis of hematopoietic stem and progenitor cells (HSCs) has been an invaluable tool in defining the biology of stem cell populations. We have recently described the production of AC133, a monoclonal antibody (MoAb) that binds to a novel cell surface antigen present on a CD34(bright) subset of human HSCs. This antigen is a glycosylated protein with a molecular weight of 120 kD. Here, we report the molecular cloning of a cDNA encoding this antigen and show that it does not share homology with any previously described hematopoietic or other cell surface antigen(s). The AC133 polypeptide has a predicted size of 97 kD and contains five-transmembrane (5-TM) domains with an extracellular N-terminus and a cytoplasmic C-terminus. Whereas the expression of tetraspan (4-TM) and 7-TM molecules is well documented on mature and immature hematopoietic cells and leukocytes, this 5-TM type of structure containing two large (255-amino acid [aa] and 290-aa) extracellular loops is unique and does not share sequence homology with any known multi-TM family members. Expression of this protein appears limited to bone marrow in normal tissue by immunohistochemical staining; however, Northern analysis suggests that the mRNA transcript is present in a variety of tissues such as the kidney, pancreas, placenta, and fetal liver. The AC133 antigen is also expressed on subsets of CD34+ leukemias, suggesting that it may be an important early marker for HSCs, as well as the first described member of a new class of TM receptors.

Selective depletion of myelin-reactive T cells with the anti-OX-40 antibody ameliorates autoimmune encephalomyelitis

The OX-40 protein was selectively upregulated on encephalitogenic myelin basic protein (MBP)-specific T cells at the site of inflammation during the onset of experimental autoimmune encephalomyelitis (EAE). An OX-40 immunotoxin was used to target and eliminate MBP-specific T cells within the central nervous system without affecting peripheral T cells. When injected in vivo, the OX-40 immunotoxin bound exclusively to myelin-reactive T cells isolated from the CNS, which resulted in amelioration of EAE. Expression of the human OX-40 antigen was also found in peripheral blood of patients with acute graft-versus-host disease and the synovia of patients with rheumatoid arthritis during active disease. The unique expression of the OX-40 molecule may provide a novel therapeutic strategy for eliminating autoreactive CD4+T cells that does not require prior knowledge of the pathogenic autoantigen.

Characterization of the epitope recognized by a mAb that reacts differentially with murine suppressor T cells

Although reliable antibodies are available that distinguish human suppressor T (Ts) cells from CTL and other T cells, few are available for murine Ts cells. We have developed a mAb (984D4.6.5) that, in the presence of complement, depletes alloantigen-specific Ts cells but not CTL. This antibody recognizes activated Ts cells but not their precursors. In these studies, flow cytometric analysis demonstrates that 984D4.6.5 reacts with several Ts cell hybridomas, cloned Ts cell lines and WEHI-3 (a myelomonocytic tumor cell line). Reactivity was not detected with BW5147, Th cell hybridomas, cloned Th cells, CTL lines and hybridomas, B cell lines, thymocytes, splenocytes, bone marrow cells nor a variety of tumor cells. Among 984D4.6.5 positive lines, expression is heterogeneous and the number of cells expressing high levels of the epitope is increased when the hybridomas are maintained at a relatively high cell density. Neuriminidase and pronase deplete the epitope recognized by mAb 984D4.6.5. Protein synthesis and glycosylation inhibitors also reduce expression of this epitope. These observations suggest that the epitope recognized by 984D4.6.5 is a carbohydrate linked to a polypeptide. This antibody was tested by ELISA for binding to a large panel of carbohydrates and glycolipids coupled to BSA. The only one that bound 984D4.6.5 was LS tetrasaccharide c (NeuNAc alpha 2-6Gal beta 1-4GlcNAc beta 1-3Gal beta 1-4Glc), an O-linked carbohydrate. Comparative analysis shows that both the sequence and the linkage of these sugars are essential to the reactivity with the 984D4.6.5 antibody. This epitope is expressed by a glycoprotein of approximately 200 kDa, as shown by Western blots. The identity of this glycoprotein remains to be determined, but indirect evidence suggests that it is not CD45.

Immunospecific vesicle targeting facilitates fusion with selected cell populations

Antibody-directed targeting of vesicles to cells dramatically enhances polyethylene glycol-mediated fusion and microinjection. Sealed erythrocyte ghosts or liposomes, containing fluorescent bovine serum albumin, were targeted to murine spleen and thymus cells, and to lymphocyte and monocyte cell lines. In all cases, targeted cell populations showed substantial levels of microinjection, whereas populations treated with the fusogen in the absence of targeting were not significantly microinjected. Attachment of vesicles to selected cells was achieved by first labelling the cells with biotin-modified antibody and then treating them with avidin-coupled sealed ghosts or liposomes. Another approach to the promotion of selective fusion aims to alter the cell recognition properties of Sendai virus so that its fusogenic activity may be redirected to specific cellular targets. The agglutination and fusion of red cells by UV-inactivated Sendai virus were completely blocked by low concentrations of a Fab preparation of a monoclonal antibody against the viral haemagglutinin (HN) sites. Agglutination and fusion activity were restored in the presence of Fab-anti-HN by providing an alternative recognition system, namely, when the virus had been coupled with biotin and the red cells with avidin. Methods for facilitating microinjection by specifically directing vesicles to target cells may be particularly useful in overcoming barriers to the transfer of genes into lymphocytes by standard transfection techniques.

Immunospecific vesicle targeting facilitates microinjection into lymphocytes

Antibody-directed targeting of vesicles to cells dramatically enhances polyethylene glycol-mediated fusion and microinjection. Sealed erythrocyte ghosts, containing fluorescent bovine serum albumin, were targeted to murine spleen and thymus cells, and to lymphocyte, monocyte, and fibroblast cell lines. In all cases, targeted cell populations showed substantial levels of microinjection, whereas populations treated with the fusogen in the absence of targeting were not significantly microinjected. To achieve attachment of vesicles to selected cells, the cells were first labeled with biotin-modified antibody then treated with sealed ghosts prepared from avidin-coupled erythrocytes. This procedure should prove useful when the injection of specific cell populations is desired, or with cell types such as lymphocytes that are difficult to fuse, or when the use of limited reagents necessitates high injection efficiencies.

Mycobacterium fortuitum infection: evidence of bactericidal defect due to hyperactive antigen-specific suppressor cells. Correction in vitro and in vivo by cholinergic agonist and indomethacin

Immunologic studies in a patient with long-standing Mycobacterium fortuitum infection revealed normal numbers of T cells, T inducers, T suppressors, B cells, and monocytes, significant in vitro proliferative response to M. fortuitum antigen, and poor bactericidal activity against M. fortuitum but not against Escherhicia coli. M. fortuitum antigen-activated suppressor cells contributed to the bactericidal defect. The activity of these suppressor cells could be eliminated by the in vitro treatment of blood mononuclear cells with a combination of a cholinergic agonist and indomethacin, but not with either alone. Administration of the two drugs to the patient resulted in reversal of the bactericidal defect and dramatic clinical improvement. Systemic atypical (nontuberculous) mycobacterial infection may activate specific suppressor cells that could compromise the host's phagocytic cell function. Modulation of those suppressor cells by a combination of a cholinergic agonist and prostaglandin synthetase inhibitor could reverse this abnormality and may be beneficial to the patient.