Risk-stratified Sequential Treatment of Post-transplant Lymphoproliferative Disease (PTLD) With Rituximab SC and Immunochemotherapy

Post-transplant lymphoproliferative disorders (PTLD) differ clinically from lymphoma in the general (immunocompetent) population due to their higher incidence and their frequent association with Epstein-Barr virus. Previous clinical trials have shown their remarkably good response to rituximab as well as to chemotherapy.

The PTLD-1 trial demonstrated the efficacy and safety of sequential immunochemotherapy with 4 courses of rituximab IV followed by 4 cycles of CHOP chemotherapy. Compared to trials of rituximab monotherapy in PTLD, median overall survival was extended from 2.4 to 6.5 years. Compared to previous trials of chemotherapy, complications were reduced. In addition, we noted that those patients who already had a good response to the first four cycles of rituximab did better overall than those who did not. As a consequence, the PTLD-1/3 trial introduced risk-stratification in sequential treatment according to the response to the first 4 courses of rituximab monotherapy. Those patients with a complete remission went on to receive four further courses of rituximab whereas those who did not received rituximab and CHOP chemotherapy. Interim results have demonstrated that it is safe to restrict chemotherapy treatment in this manner and thus established the concept of treatment stratification based on the response to rituximab.

The PTLD-2 trial is the next step in the development of this strategy. Compared to the PTLD-1/3 trial, the key difference is the use of subcutaneous instead of intravenous rituximab application. Interim results from an ongoing trial of patients with follicular lymphoma (NCT01200758) have shown that subcutaneous administration results in increased blood levels and in non-inferior remission rates. Furthermore, the stratification strategy is refined based on observations from the previous PTLD-1 and PTLD1/3 trials: Risk groups are now defined not only based on response to rituximab therapy but also on the international prognostic index (IPI, a well-established lymphoma risk score) and the transplanted organ. The major advantage of this new stratification is an extended low-risk group that is eligible for subcutaneous rituximab monotherapy: Patients with a low risk of disease progression, defined as those who achieve a complete remission after the first four courses of subcutaneous rituximab monotherapy and those with an IPI of 0 to 2 who achieve a partial remission at interim staging, will go on with rituximab monotherapy. Patients with high IPI who achieve a partial remission, patients with stable disease at interim staging and non-thoracic transplant recipients with progressive disease at interim staging will be considered high risk. These patients will go on with 4 cycles of rituximab plus CHOP chemotherapy similar to the PTLD-1/3 protocol. Thoracic transplant recipients refractory to rituximab will be considered very high risk and will go on with rituximab subcutaneous plus alternating chemotherapy with CHOP and DHAOx.

The trial hypothesis is that the new protocol will improve the event-free survival, a measure integrating unfavorable events such as death, disease progression and treatment complications, particularly infections, in the low risk-group compared to the results of the PTLD-1 trial. In very high-risk patients data from the PTLD-1 and PTLD-1/3 trial have shown that the current treatment is not sufficient to control the disease. Death due to disease progression was observed in more than 80% of patients. Here, rituximab combined with alternating chemotherapy cycles of CHOP and DHAOx (+GCSF) may increase treatment efficacy with an acceptable toxicity profile.

In summary, the PTLD-2 trials tests if the substitution of subcutaneous for intravenous rituximab and an updated stratification strategy that deescalates treatment for those at low risk and escalates treatment for those at very high risk can further improve the overall efficacy and safety of PTLD therapy.