The use of PTCy as GvHD prophylaxis in patients treated with checkpoint inhibitors prior to allo-HCT improves outcomes

Programmed cell death protein-1 (PD-1) inhibition has previously been shown to induce responses in patients with relapsed or refractory (R/R) lymphoproliferative neoplasms,¹ acute myeloid leukemia (AML), and myelodysplastic syndromes (MDS).² Patients who failed this treatment and subsequently relapse, typically undergo allogeneic hematopoietic cell transplantation (allo-HCT). However, concerns have been raised on the safety of using anti-PD-1 inhibitors before transplantation due to a potential increased risk of graft-versus-host disease (GvHD) by enhancing effector T-cell response; although there is evidence suggesting better graft-versus-leukemia effect with prior use of PD-1 blockade in the same setting. GvHD prophylaxis with posttransplant cyclophosphamide (PTCy) have been shown to suppress clonal alloreactive effector T cells and enhance the role of regulatory T cells (Tregs), which could counterbalance the effect of PD-1 inhibition.¹

In the  first study recently published in Leukemia, Juan Nieto and colleagues compared PTCy-based GvHD prophylaxis with tacrolimus/sirolimus in patients with non-Hodgkin lymphoma (NHL) treated with an anti-PD-1 inhibitor, nivolumab, prior to allo-HCT.¹ Similarly, a second study was published in Cancer (Betül Oran et al.), which is a retrospective investigation on the outcomes after GvHD prophylaxis with PTCy in patients with AML and/or MDS who were treated with an anti-PD-1, and/or an anti-cytotoxic T-lymphocyte-associated protein 4, monoclonal antibodies prior to transplant.² Herein we will be providing data from both these studies.

Nieto et al.: Comparing GvHD prophylaxis with PTCy vs tacrolimus/sirolimus in allo-transplanted patients with NHL who had received prior therapy with nivolumab

Method¹

• Patients diagnosed with lymphoid malignancies who receiving allo-HCT from 10/10 HLA matched related and unrelated donors, were prospectively assessed between 2017 and 2019
• Further subgroup analysis compared reduced-intensity or non-myeloablative conditioning and GvHD prophylaxis (with tacrolimus/sirolimus or PTCy-sirolimus-mycophenolate mofetil)
• Peripheral blood mononuclear cells and plasma samples were collected and cryopreserved on Days 0 (prior to infusion), +7, +14, +21, +28, and +56 after allo-HCT, to assess T-cell activation
• ELISA tests were used to follow nivolumab concentrations in the plasma over time

Results

• A total of 18 patients were investigated; six had received nivolumab before allo-HCT, 12 were nivolumab-naïve
  • Nivolumab dose was 3 mg/kg with a median of eight doses (range, 4–11)
• The outcomes of patients that received nivolumab prior to transplant, after a median follow-up of 29 months (range, 5–57), is shown in Table 1 

Table 1. A comparison of the outcomes with nivolumab exposure and PTCy/tacrolimus treatment in terms of safety and efficacy¹

aGvHD, acute graft-versus-host disease; Sir, sirolimus; Tac, tacrolimus; MMF, mycophenolate mofetil; PTCy, posttransplant cyclophosphamide
Patients (N = 18)	Nivolumab exposure	GvHD prophylaxis	aGvHD Grade 3–4 (n)	Disease relapse (n)	Outcome (n)
3	Exposed	Tac/Sir	3	0	Dead (3)
3	Exposed	Sir/MMF/PTCy	0	2	Alive (2), dead (2)
6	naïve	Tac/Sir	1	0	Alive (6)
6	naïve	Sir/MMF/PTCy	2	1	Alive (3), dead (3)

• No chronic GvHD was reported from the entire cohort (N = 18)
• ELISA analysis showed that all nivolumab-exposed patients had detectable levels of the drug until Day +56 after allo-HCT. At Day +21 after allo-HCT, residual nivolumab was able to induce T-cell activation by binding and blocking PD-1 on T cells; this was differentially modulated depending on the administered GvHD prophylaxis
• To assess the capacity of residual nivolumab of binding to PD-1 on allogeneic T cells, the investigators incubated peripheral blood mononuclear cells from age-matched healthy people with plasma from nivolumab-exposed and -naïve patients, and observed a lower expression of PD-1 on CD4 and CD8 T cells in nivolumab-exposed patients vs nivolumab-naïve patients
• a lower CD4:CD8 ratio and Treg:CD8 ratio was observed in nivolumab-exposed vs nivolumab-naïve patients in the group that received tacrolimus/sirolimus. In contrast, in nivolumab exposed patients who received PTCy-based regimen, the Treg:CD8 ratio was higher compared to nivolumab naïve patients. The lower Treg:CD8 ratio coupled with an unbalanced recovery of regulatory T-cell homeostasis was associated with a higher risk of GvHD in patients receiving allo-HCT and PD-1 inhibitors
• A higher proportion of IFN-γ-producing CD4 and CD8 T cells and a greater Th1 differentiation were observed in nivolumab-exposed patients receiving tacrolimus/sirolimus vs nivolumab-naïve patients. The production of IFN-γ by T cells and Th subsets in patients receiving the PTCy treatment were similar between nivolumab-exposed and -naïve patients. This observation is supported by recent data that suggests that even with circulating nivolumab in the plasma, PTCy abrogates nivolumab-induced immune activation

Betül Oran et al.: PTCy improves transplantation outcomes in patients with AML/MDS previously treated with checkpoint inhibitors

Study design and patient characteristics

• Patients who received nivolumab and/or ipilimumab for the treatment of AML and/or MDS, and underwent allo-HCT at The University of Texas, MD Anderson Cancer Center, were retrospectively analyzed. This investigation was based on data from four clinical trials (NCT02530463, NCT02397720, NCT02464657, and NCT02532231) between April 2015 and December 2017.
• The trial cohort included patients with active disease at the time of allo-HCT (63%) and high-risk cytogenetics (47%).
• Patients received a median number of four (range, 1–14 treatments) checkpoint inhibitor (CPI; nivolumab and/or ipilimumab) treatments, prior to allo-HCT.
• GvHD prophylaxis used was either tacrolimus and mini-methotrexate with or without antithymocyte globulin (49%) or PTCy at a dose of 50 mg/kg on Days +3 and +4, and tacrolimus with or without mycophenolate mofetil (51%; n = 22). The donor type determined the GvHD prophylaxis used. PTCy was given to all haploidentical donor recipients but not to the cord blood recipients. PTCy was also given to 10 of the 25 matched unrelated recipients, and four of the seven matched related recipients.

Results

• Of the total 43 patients analysed, 22 with AML and/or MDS had received CPI prior to allo-HSCT and were treated with PTCy. The 6-month outcomes were significantly superior in patients treated with PTCy compared with those who did not receive PTCy (shown in Table 2)
• Multivariant analysis confirmed that 1-year progression-free survival was better in patients who had PTCy compared with those who did not have PTCy (HR, 0.3; 95% CI, 0.1–0.8; p = 0.02)
• Within the first 6 months following allo-HCT there was no disease progression observed in the PTCy group
• The 1-year progression-free survival and overall survival rates were similar between the GvHD prophylaxis arms for patients without prior CPI exposure
• In contrast, in patients who had prior CPI exposure before receiving allo-HCT, those who did not receive PTCy had the worst outcome (Table 2); however, this was not statistically significant

Table 2. A comparison of the outcomes with prior CPI exposure and PTCy treatment²

Allo-HCT, allogeneic hematopoietic cell transplantation; CPI, checkpoint inhibitor; NRM, non-relapse mortality; OS, overall survival; PFS, progression-free survival; PTCy, posttransplant cyclophosphamide
	Prior CPI to allo-HCT + PTCy (n = 22)	Prior CPI to allo-HCT + no PTCy (n = 21)	No prior CPI + PTCy (n = 40)	No prior CPI + no PTCy (n = 42)
6-month OS, % (95% CI)	81 (51–94)	60 (36–78)	—	—
6-month PFS, % (95% CI)	81 (51–94)	50 (27–69)	—	—
6-month NRM, % (95% CI)	14 (4–51)	25 (12–53)	—	—
1-year OS, % (95% CI)	83 (56–94)	28 (10–48)	53 (29–71)	55 (37–69)
1-year PFS, % (95% CI)	40 (15–64)	23 (7–43)	50 (28–69)	44 (28–59)

• The interval between CPI and allo-HCT did not impact the incidence of acute GvHD (aGvHD)
• Patients who received > 4 treatments with CPI prior to allo-HCT, and had received GvHD prophylaxis without PTCy had the highest incidence of Grade 2–4 and Grade 3–4 aGvHD (86% and 43%, respectively)
• In a case control matching analysis comparing the 43 CPI-exposed patients with 82 CPI-naïve patients, there was a greater risk of Grade 3–4 aGvHD by Day 100 observed with the prior use of CPI. This significantly increased risk, applied only to patients with prior CPI exposure who did not receive PTCy (Table 3)
• Regardless of CPI exposure prior to allo-HCT, similar Grade 2–4 aGvHD incidences by Day 100 were observed, independent of the GvHD prophylaxis used (Table 3)
• These data support the results of other studies and demonstrate treatment with PTCy results in a decreased incidence of severe GvHD, that may not jeopardize the graft-versus-leukemia effect

Table 3. Incidence of aGvHD²

Allo-HCT, allogeneic hematopoietic cell transplantation; CPI, checkpoint inhibitor; aGvHD, acute graft-versus-host disease; PTCy, posttransplant cyclophosphamide
Patients	Patients not treated with CPI (n = 82)		Patients treated with CPI (n = 43)
	Incidence, %	95% CI	Incidence, %	95% CI	HR	95% CI
Day 100 Grade 2–4 aGvHD
Overall	49	(39–62)	49	(35–68)	0.9	0.5–1.6
PTCy	52	(38–71)	44	(26–75)	0.7	0.3–1.6
No PTCy	47	(34–66)	54	(35–82)	1.1	0.5–2.4
Day 100 Grade 3–4 aGvHD
Overall	3	(1–10)	13	(6–30)	5.2	0.9–27
PTCy	3	(1–19)	5	(1–35)	2.0	0.1–31
No PTCy	3	(1–18)	22	(9–51)	8.5	0.9–79

Conclusions

Both studies confirm that the use of CPI prior to allo-HSCT favors the development of GvHD, possibly due to the persistent presence of CPI after transplantation, generating enhanced T-cell activation. Juan Nieto and colleagues demonstrated that the extent of T-cell activation is dependent on the GvHD prophylactic regimen used, and can be alleviated, to a degree, with PTCy treatment in patients with NHL. Similarly, Betül Oran et al, reported encouraging data that supports the use of PTCy as a GvHD prophylaxis to decrease GvHD incidence whilst maintaining the graft-versus-leukemia effect in patients with AML/MDS who received CPI before undergoing allo-HCT, which appears to lead to improved transplantation outcomes.  

Limitations  

• Limited number of patients^{1 ,2}