CAR-T Cell Therapy for Lymphoma: How Does Radiation Therapy Fit In?

Role of radiation in chimeric antigen receptor T-cell therapy for patients with relapsed/refractory non-Hodgkin lymphoma: Current studies and future prospects

Chimeric antigen receptor T-cell (CAR-T) therapy has revolutionized the treatment approach for patients with relapsed/refractory non-Hodgkin lymphoma (R/R NHL). However, the long-term prognosis has been discouraging. Moreover, the urgent resolution of two critical issues is necessary: minimize tumor burden before CAR-T infusion and control fatal toxicities post CAR-T therapy. By combining radiotherapy (RT), the safety and efficacy of CAR-T can be improved. RT can serve as bridging therapy, reducing the tumor burden before CAR-T infusion, thus enabling safe and successful CAR-T infusion, and as salvage therapy in cases of CAR-T therapy failure. This review aims to discuss the current evidence supporting the use of RT in CAR-T therapy for patients with R/R NHL. Although most studies have shown a positive role of RT in combined modality treatments for patients undergoing CAR-T therapy, the synergy gained from these remains uncertain. Furthermore, the optimal dose/fraction and radiation response require further investigation.

The progress of novel strategies on immune-based therapy in relapsed or refractory diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) can be cured with standard front-line immunochemotherapy, whereas nearly 30-40% of patients experience refractory or relapse. For several decades, the standard treatment strategy for fit relapsed/refractory (R/R) DLBCL patients has been high-dose chemotherapy followed by autologous hematopoietic stem cell transplant (auto-SCT). However, the patients who failed in salvage treatment or those ineligible for subsequent auto-SCT have dismal outcomes. Several immune-based therapies have been developed, including monoclonal antibodies, antibody-drug conjugates, bispecific T-cell engaging antibodies, chimeric antigen receptor T-cells, immune checkpoint inhibitors, and novel small molecules. Meanwhile, allogeneic SCT and radiotherapy are still necessary for disease control for fit patients with certain conditions. In this review, to expand clinical treatment options, we summarize the recent progress of immune-related therapies and prospect the future indirections in patients with R/R DLBCL.

Time to abandon CAR-T monotherapy for solid tumors

In recent decades, chimeric antigen receptor T (CAR-T) cell therapy has achieved dramatic success in patients with hematological malignancies. However, CAR-T cell therapy failed to effectively treat solid tumors as a monotherapy. By summarizing the challenges of CAR-T cell monotherapy for solid tumors and analyzing the underlying mechanisms of combinatorial strategies to counteract these hurdles, we found that complementary therapeutics are needed to improve the scant and transient responses of CAR-T cell monotherapy in solid tumors. Further data, especially data from multicenter clinical trials regarding efficacy, toxicity, and predictive biomarkers are required before the CAR-T combination therapy can be translated into clinical settings.

Assessing the role of radiotherapy in patients with refractory or relapsed high-grade B-cell lymphomas treated with CAR T-cell therapy

An estimated 30-40% of patients with diffuse large B cell lymphoma (DLBCL) will either relapse or have refractory disease with first-line chemoimmunotherapy. The standard approach for relapsed/refractory disease is salvage chemotherapy followed by autologous stem cell transplantation, but this approach cures fewer than 20% of patients in the modern era. This low cure rate is a result of refractory disease despite salvage therapy, medical ineligibility for transplantation, or relapse following transplantation. CD19-targeted chimeric antigen receptor (CAR) T-cell therapy has revolutionized the treatment paradigm for patients with relapsed or refractory disease, leading to response rates that range between 52% to 93%, and overall survival rates at one year between 48% and 83%. However, the time from apheresis to infusion of CAR T-cell therapy currently takes several weeks, leaving many patients in need of bridging therapy to control disease progression. Radiation therapy (RT) has been utilized as a bridging therapy prior to CAR T infusion in select patients, with some remarkable responses in chemorefractory disease. Furthermore, the potential synergy between RT and CAR T-cells due to immunomodulatory mechanisms has generated considerable excitement, as it has been hypothesized that RT could also be considered as a salvage therapy following CAR T failure, based on limited case series published to date. Prospective trials are warranted to validate the significance of this modality following CAR T-cell therapy.

Does bridging radiation therapy affect the pattern of failure after CAR T-cell therapy in non-Hodgkin lymphoma?

PURPOSE

Analyze the pattern of disease failure after anti-CD19-directed chimeric antigen receptor T-cell therapy (CART) for non-Hodgkin lymphoma, assess the local control rate of bridging radiotherapy (bRT) and characterize in-field recurrences.

METHODS

We retrospectively reviewed 120 patients with NHL who received CART between 2018 and 2020. Baseline characteristics and treatment outcomes were compared between patients who received bRT and those who did not (noRT).

RESULTS

Of the 118 patients included, 14 (12%) received bRT, while 104 (88%) did not. bRT group had more localized and extranodal disease. bRT was delivered with a median dose of 20 Gy (range: 15-36) in 5 fractions (range: 3-24). Pattern of failure analysis revealed that progression involving pre-existing sites was the predominant pattern of failure in both the bRT and noRT groups (86% and 88%, respectively). Median duration of response was 128 days (range: 25-547) for bRT group and 93 days (range: 22-965) for noRT group (p = 0.78). In the bRT group, only 2/15 sites irradiated had infield recurrence and where characterized by bulky disease, SUV_max >20, elevated LDH at the time of CART infusion, and extranodal involvement. The bRT 1-year LC was 86%. Median duration of local response was 257 days (range: 25-630) for radiation-bridged sites.

CONCLUSION

Majority of progressions after CART infusion involve pre-existing sites. Bridging RT prior to CART provides excellent in-field local control and durable response. Patients with bulky disease, SUV_max >20, elevated LDH, and extranodal involvement are likely at higher risk of in-field recurrence after bRT and may benefit from higher curative doses of bRT.

Radiation and CAR T-cell Therapy in Lymphoma: Future Frontiers and Potential Opportunities for Synergy

CAR T-cell therapy has revolutionized the treatment approach to patients with relapsed/refractory hematologic malignancies; however, there continues to be opportunity for improvement in treatment toxicity as well as response durability. Radiation therapy can play an important role in combined modality treatments for some patients undergoing CAR T-cell therapy in various clinical settings. In this review, we discuss the current evidence for RT in the setting of CAR T-cell therapy for patients with hematologic malignancies and propose potential opportunities for future investigation of RT and CAR T-cell treatment synergy. Future research frontiers include investigation of hypotheses including radiation priming of CAR T-cell mediated death, pre-CAR T-cell tumor debulking with radiation therapy, and selection of high risk patients for early radiation salvage after CAR T cell therapy.

Proton Therapy as a Bridging Treatment in CAR T-Cell Therapy for Relapsed and Refractory Large B-Cell Lymphoma: Is There a Role?

Diffuse large B-cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma. Since the relapse rate of DLBCL to frontline chemoimmunotherapy and salvage autologous hematopoietic cell transplant is high, CD19-directed chimeric antigen receptor (CAR) T-cell therapy was adopted. Given the time interval needed for CAR T cells to be manufactured (3-5 weeks) and the aggressiveness of these relapsed/refractory lymphomas, some patients do not make it to the CAR T-cell infusion phase. This calls for a bridging therapy to control, debulk, and sensitize the disease during this period. Radiation therapy can serve this purpose and has shown promising results in some studies. Proton therapy, compared to standard radiation therapy, in some locations, can reduce the radiation dose to the organs at risk, which may lead to fewer side effects for patients with lymphomas. Thus, we hypothesize that proton therapy may serve as a promising bridging strategy to CAR T-cell therapy for some patients.