Eric L. Sievers

Purpose:TTI-621 (SIRPα-IgG1 Fc) is a novel checkpoint inhibitor that activates antitumor activity by blocking the CD47 “don't eat me” signal. This first-in-human phase I study (NCT02663518) evaluated the safety and activity of TTI-621 in relapsed/refractory (R/R) hematologic malignancies.Patients and Methods:Patients with R/R lymphoma received escalating weekly intravenous TTI-621 to determine the maximum tolerated dose (MTD). During expansion, patients with various malignancies received weekly single-agent TTI-621 at the MTD; TTI-621 was combined with rituximab in patients with B-cell non-Hodgkin lymphoma (B-NHL) or with nivolumab in patients with Hodgkin lymphoma. The primary endpoint was the incidence/severity of adverse events (AEs). Secondary endpoint included overall response rate (ORR).Results:Overall, 164 patients received TTI-621: 18 in escalation and 146 in expansion (rituximab combination, n = 35 and nivolumab combination, n = 4). On the basis of transient grade 4 thrombocytopenia, the MTD was determined as 0.2 mg/kg; 0.1 mg/kg was evaluated in combination cohorts. AEs included infusion-related reactions, thrombocytopenia, chills, and fatigue. Thrombocytopenia (20%, grade ≥3) was reversible between doses and not associated with bleeding. Transient thrombocytopenia that determined the initial MTD may not have been dose limiting. The ORR for all patients was 13%. The ORR was 29% (2/7) for diffuse large B-cell lymphoma (DLBCL) and 25% (8/32) for T-cell NHL (T-NHL) with TTI-621 monotherapy and was 21% (5/24) for DLBCL with TTI-621 plus rituximab. Further dose optimization is ongoing.Conclusions:TTI-621 was well-tolerated and demonstrated activity as monotherapy in patients with R/R B-NHL and T-NHL and combined with rituximab in patients with R/R B-NHL.

Purpose:TTI-621 (SIRPα-IgG1 Fc) is a novel checkpoint inhibitor that activates antitumor activity by blocking the CD47 “don't eat me” signal. This first-in-human phase I study (NCT02663518) evaluated the safety and activity of TTI-621 in relapsed/refractory (R/R) hematologic malignancies.Patients and Methods:Patients with R/R lymphoma received escalating weekly intravenous TTI-621 to determine the maximum tolerated dose (MTD). During expansion, patients with various malignancies received weekly single-agent TTI-621 at the MTD; TTI-621 was combined with rituximab in patients with B-cell non-Hodgkin lymphoma (B-NHL) or with nivolumab in patients with Hodgkin lymphoma. The primary endpoint was the incidence/severity of adverse events (AEs). Secondary endpoint included overall response rate (ORR).Results:Overall, 164 patients received TTI-621: 18 in escalation and 146 in expansion (rituximab combination, n = 35 and nivolumab combination, n = 4). On the basis of transient grade 4 thrombocytopenia, the MTD was determined as 0.2 mg/kg; 0.1 mg/kg was evaluated in combination cohorts. AEs included infusion-related reactions, thrombocytopenia, chills, and fatigue. Thrombocytopenia (20%, grade ≥3) was reversible between doses and not associated with bleeding. Transient thrombocytopenia that determined the initial MTD may not have been dose limiting. The ORR for all patients was 13%. The ORR was 29% (2/7) for diffuse large B-cell lymphoma (DLBCL) and 25% (8/32) for T-cell NHL (T-NHL) with TTI-621 monotherapy and was 21% (5/24) for DLBCL with TTI-621 plus rituximab. Further dose optimization is ongoing.Conclusions:TTI-621 was well-tolerated and demonstrated activity as monotherapy in patients with R/R B-NHL and T-NHL and combined with rituximab in patients with R/R B-NHL.

Purpose: TTI-621 (SIRPα-IgG1 Fc) is a novel checkpoint inhibitor that activates antitumor activity by blocking the CD47 “don't eat me” signal. This first-in-human phase I study (NCT02663518) evaluated the safety and activity of TTI-621 in relapsed/refractory (R/R) hematologic malignancies. Patients and Methods: Patients with R/R lymphoma received escalating weekly intravenous TTI-621 to determine the maximum tolerated dose (MTD). During expansion, patients with various malignancies received weekly single-agent TTI-621 at the MTD; TTI-621 was combined with rituximab in patients with B-cell non-Hodgkin lymphoma (B-NHL) or with nivolumab in patients with Hodgkin lymphoma. The primary endpoint was the incidence/severity of adverse events (AEs). Secondary endpoint included overall response rate (ORR). Results: Overall, 164 patients received TTI-621: 18 in escalation and 146 in expansion (rituximab combination, n = 35 and nivolumab combination, n = 4). On the basis of transient grade 4 thrombocytopenia, the MTD was determined as 0.2 mg/kg; 0.1 mg/kg was evaluated in combination cohorts. AEs included infusion-related reactions, thrombocytopenia, chills, and fatigue. Thrombocytopenia (20%, grade ≥3) was reversible between doses and not associated with bleeding. Transient thrombocytopenia that determined the initial MTD may not have been dose limiting. The ORR for all patients was 13%. The ORR was 29% (2/7) for diffuse large B-cell lymphoma (DLBCL) and 25% (8/32) for T-cell NHL (T-NHL) with TTI-621 monotherapy and was 21% (5/24) for DLBCL with TTI-621 plus rituximab. Further dose optimization is ongoing. Conclusions: TTI-621 was well-tolerated and demonstrated activity as monotherapy in patients with R/R B-NHL and T-NHL and combined with rituximab in patients with R/R B-NHL.

Sézary syndrome (SS), the leukemic variant of cutaneous T-cell lymphoma, has limited treatment options and rare occurrences of long-term remission, thus warranting research into new treatment approaches. CD47 has emerged as a promising target for multiple tumor types, but its role in SS remains unknown. Here, we show that CD47 is highly expressed on Sézary cells in the peripheral blood and skin, and the high level of CD47 expression correlates with worse overall survival (OS) in patients with SS. We also demonstrate that CD47 expression on Sézary cells is under the influence of interleukin 4 (IL-4), IL-7, and IL-13. Signal regulatory protein αFc (SIRPαFc; TTI-621), a novel CD47 decoy receptor, triggers macrophage-mediated phagocytosis of Sézary cells and, when administered in clinical trial settings, results in significant tumor load reduction. We conclude that inhibition of the CD47-SIRPα signaling pathway has therapeutic benefit for patients with SS. This trial was registered at www.clinicaltrials.gov as #NCT02663518.

Purpose: The ubiquitously expressed transmembrane glycoprotein CD47 delivers an anti-phagocytic (do not eat) signal by binding signal-regulatory protein α (SIRPα) on macrophages. CD47 is overexpressed in cancer cells and its expression is associated with poor clinical outcomes. TTI-621 (SIRPαFc) is a fully human recombinant fusion protein that blocks the CD47–SIRPα axis by binding to human CD47 and enhancing phagocytosis of malignant cells. Blockade of this inhibitory axis using TTI-621 has emerged as a promising therapeutic strategy to promote tumor cell eradication. Experimental Design: The ability of TTI-621 to promote macrophage-mediated phagocytosis of human tumor cells was assessed using both confocal microscopy and flow cytometry. In vivo antitumor efficacy was evaluated in xenograft and syngeneic models and the role of the Fc region in antitumor activity was evaluated using SIRPαFc constructs with different Fc tails. Results: TTI-621 enhanced macrophage-mediated phagocytosis of both hematologic and solid tumor cells, while sparing normal cells. In vivo, TTI-621 effectively controlled the growth of aggressive AML and B lymphoma xenografts and was efficacious in a syngeneic B lymphoma model. The IgG1 Fc tail of TTI-621 plays a critical role in its antitumor activity, presumably by engaging activating Fcγ receptors on macrophages. Finally, TTI-621 exhibits minimal binding to human erythrocytes, thereby differentiating it from CD47 blocking antibodies. Conclusions: These data indicate that TTI-621 is active across a broad range of human tumors. These results further establish CD47 as a critical regulator of innate immune surveillance and form the basis for clinical development of TTI-621 in multiple oncology indications. Clin Cancer Res; 23(4); 1068–79. ©2016 AACR.

Background: Independent central review of clinical imaging remains the standard for oncology clinical trials with registration potential. A limited independent central review strategy has been proposed for solid tumor trials based on concordance between central and local evaluation of response. Concordance between independent central review and local evaluation of response in hematological malignancies is not known. Methods: We retrospectively evaluated concordance between prospectively performed central and local assessments of response using the Revised Response Criteria for Malignant Lymphoma across two international, open-label, single-arm, registration studies of brentuximab vedotin in patients with relapsed or refractory Hodgkin lymphoma (N = 102) or systemic anaplastic large-cell lymphoma (N = 58). Results: Overall objective response rates were similar between assessors for both the trial in Hodgkin lymphoma (75% independent central review, 72% local evaluation) and the trial in anaplastic large-cell lymphoma (86% independent central review, 83% local evaluation). Patient-specific objective response concordance was also substantial (Hodgkin lymphoma: kappa = 0.68; anaplastic large-cell lymphoma: kappa = 0.74). Median progression-free survival was similar between assessors for patients with anaplastic large-cell lymphoma (14.3 months by independent central review (95% confidence interval: 6.9, -); 14.5 months by local evaluation (95% confidence interval: 9.4, -)), but longer by local evaluation in patients with Hodgkin lymphoma (5.8 months by independent central review (95% confidence interval: 5.0, 9.0); 9.0 months by local evaluation (95% confidence interval: 7.1, 12.0)). Median duration of response was longer by local evaluation in both malignancies, which was primarily attributable to earlier computed tomography and positron emission tomography–based scoring of progression by independent central review. Conclusion: A limited independent review audit strategy for clinical trials of some lymphomas appears feasible and practical based on substantial concordance in assessments of overall objective response by central and local evaluation in two international, prospective, registration trials in lymphoma. Some variability between assessors in the time-to-event endpoints was observed, which appeared attributable to earlier assignments of progression by independent central review compared with local evaluation.

TPS7585 Background: TTI-621 (SIRPαFc) is a soluble recombinant fusion protein designed to bind human CD47 and prevent it from delivering an inhibitory signal to macrophages. TTI-621 is created by combining the sequences encoding the N-terminal portion of human SIRPα with the Fc region of human IgG1. The SIRPα region interacts with its ligand CD47, while the Fc region binds to macrophage Fcγ receptors. High levels of CD47 expression are observed on many different tumor types, where its expression is often associated with poor prognosis. It is hypothesized that tumor cells exploit the suppressive CD47-SIRPα axis to evade macrophage-mediated destruction. TTI-621 is thought to function as a decoy receptor, binding CD47 on tumor cells and blocking its anti-phagocytic signal, allowing macrophages to ingest malignant cells. In vitro studies have shown that TTI-621 promotes macrophage-mediated phagocytosis of a range of hematologic tumor cells and selectively induces phagocytosis of malignant cells over normal cells. TTI-621 has also shown potent antitumor activity in preclinical AML and B-cell lymphoma xenograft models. Methods: The objective of this phase 1, open label, multicenter study (TTI-621-01) is to evaluate the safety and tolerability, and to identify the maximum tolerated dose of intravenously-delivered TTI-621 in subjects with relapsed/refractory lymphoma using a 3+3 dose-escalation study design. Once the optimal dose has been determined in the dose-escalation phase, multiple expansion cohorts of subjects with a wide variety of relapsed/refractory hematologic malignancies will be enrolled. Pharmacokinetics, immunogenicity, and antitumor activity will also be evaluated. Eligible subjects are adults with advanced, measurable, hematologic malignancies, which have progressed on standard anticancer therapy or for which no other approved therapy exists. Subjects with cutaneous T-cell lymphoma, high grade lymphoma, and AML M3 are excluded. TTI-621 will be administered IV once weekly at protocol-defined doses starting at 0.05 mg/kg. Treatment may continue until disease progression, unacceptable toxicity, or other reason for discontinuation (NCT02663518). Clinical trial information: NCT02663518.