Lymphodepletion optimization for CAR T-cell therapy

Chimeric antigen receptor (CAR) T-cell therapy is becoming more common in the treatment of both hematological and solid tumors. Prior to infusion, lymphodepletion is frequently performed, however, no standardized protocol exists for this procedure. During the eighth annual meeting of the Society of Hematologic Oncology (SOHO), Elizabeth Budde presented how this process can be optimized to aid persistence and efficacy of infused CAR T cells.¹

Why use lymphodepletion?

Lymphodepletion leads to lymphopenia, affecting T, B, and NK cells, and it has multiple positive effects prior to CAR T-cell therapy:

• Debulking of the tumor
• Alteration of tumor phenotype
  • Decreased production of certain metabolites
  • Change in expression of costimulatory molecules

• Modified tumor microenvironment
  • Reduced regulatory T-cells and damage to vascular endothelial cells make the environment more hospitable to CAR T cells
• Removal of cytokine sinks
  • Greater availability of interleukin (IL)-2, IL-7, and IL-15
• Suppression of host immune system
  • Decreased immunogenicity and increased persistence of infused CAR T cells

Negatives effects of lymphodepletion include the following:

• Neutropenia, anemia, thrombocytopenia, and immunosuppression, leading to a greater risk of infection
• Specific toxicities associated with lymphodepletion agents
  • Fludarabine (Flu): fevers and neurotoxicity
  • Cyclophosphamide (Cy): hemorrhagic cystitis, pericarditis, and neurotoxicity
  • Use of these agents may increase the risk of developing secondary malignancies

What is the ideal lymphodepletion regimen?

Cy/Flu combination was compared with Cy alone. Lymphodepletion with the combined treatment of Cy/Flu increased CD19 CAR T-cell expansion and resulted in greater persistence both in CD4 and CD8 cells. In addition, following a second infusion of CAR T cells, Cy/Flu treatment resulted in a second peak with significant cell expansion and longer persistence. On the contrary, when using Cy treatment alone, the second round of CAR T-cell treatment resulted in no cell persistence extension, potentially due to immune rejection.

A study published in 2018 by C. A. Ramos, et al.,² reported that patients with B-cell lymphoma treated with CAR T-cell therapy who did not undergo pre-infusion lymphodepletion therapy had a very poor cell expansion. The increased CAR T-cell expansion and persistence with the Cy/Flu regimen have also been associated with improved clinical outcomes, and the degree of persistence is related to the level of improvement.

How can the lymphodepletion regimen be optimized?

While high-dose lymphodepletion can be useful in some cases, it is important to keep in mind the associated toxicity of the agents being used. Another option explored is to change the agent rather than increasing the dose. A recent study by C. A. Ramos, et al.,³ compared the safety of bendamustine alone, bendamustine + Flu, and Cy/Flu before the infusion of CD30 CAR T-cell therapy in patients with Hodgkin lymphoma.

The lymphodepletion dosages were as follows:

• Bendamustine 90 mg/m²/day for 2 days
• Bendamustine 70 mg/m²/day + Flu 30 mg/m²/day for 3 days
• Cy 500 mg/m²/day + Flu 30 mg/m²/day for 3 days

In this study, lymphodepletion with bendamustine + Flu resulted in longer persistence of CAR T cells compared with Cy/Flu. In addition, bendamustine + Flu was shown to significantly increase the level of circulating IL-15 and IL-17 compared with bendamustine alone (p < 0.05). These beneficial anti-tumor effects of bendamustine + Flu can be seen in the impact on survival outcomes since it significantly increased progression-free survival compared with bendamustine alone or Cy/Flu (p = 0.0004). The study concluded that Flu is essential as part of the lymphodepletion regimen. Read the complete report here.

Table 1. Alternative methods for optimization of lymphodepletion beyond bendamustine in patients with lymphoma¹

Axi-cel, axicabtagene ciloleucel; CAR, chimeric antigen receptor.
Method	Study example	Goal
Addition a checkpoint inhibitor	ALEXANDER (AUTO-3)	Increase CAR T-cell activity and persistence
Addition of rituximab	ZUMA-14 (axi-cel)	Increased anti-lymphoma effect and CAR T-cell persistence
Addition of anti-CD52 monoclonal antibody	ALPHA (Allo-501)	Increased anti-lymphoma effect and CAR T-cell persistence

The ALPHA study (NCT03939026), as mentioned in Table 1, used Allo-647, a monoclonal antibody against CD52, for the lymphodepletion of patients (N = 22) with relapsed/refractory diffuse large B-cell lymphoma. Allo-647 was administered alongside Flu/Cy in 3 different treatment arms:

• Low dose Allo-647 (13 mg/day) + Cy (300 mg/m²/day) for 3 days + Flu (30 mg/m²/day)
• Concomitant Allo-647 (30 mg/day) + Cy/Flu for 3 days
• Staggered Allo-647 (30 mg/day) + Cy/Flu for 3 days

The preliminary report was with a median follow-up time of 3.8 months (range, 0.7−6.1 months). Although the number of patients evaluated was small, the higher dose of Allo-647 was associated with more significant suppression of endogenous T cells and a higher complete response rate (50% versus 27%) than the lower dose. Read the full report here.

Conclusion

Lymphodepletion before CAR T-cell therapy effectively prolongs the persistence of infused cells and increases the effectiveness of the treatment of tumors. Fludarabine is a critical component of a lymphodepletion regimen and greatly contributes to the efficacy of the procedure. While Flu/Cy is effective in multiple tumor types, there is still scope for optimization for specific cancers, ensuring that the potential toxicities of the agents used are balanced with the benefits of treatment.