Early, intriguing research suggests that preventing acute graft-versus-host disease (GVHD) in the gut – a potentially life-threatening complication of allogeneic hematopoietic cell transplantation (allo-HCT) – could be accomplished by the administration of a single antibody that targets the anti-DLL4 Notch signaling pathway, without compromising the stem cell transplant.
“The major surprise was that none of the anti–DLL4-treated animals developed acute gastrointestinal GVHD for the entire duration of the study. This was a remarkable finding, given that intestinal GVHD is otherwise seen in the vast majority of nonhuman primate transplant recipients that receive either no prophylaxis, or prophylaxis with agents other than anti-DLL4 antibodies,” co–senior author Ivan Maillard, MD, PhD, a professor of medicine and vice chief for research in hematology-oncology at the University of Pennsylvania, Philadelphia, said in an interview.
“The timing was critical,” the authors noted in the study, recently published in Science Translational Medicine. “Intervening before any symptoms of GvHD appear made the long-term protection possible.”
While GVHD may be mild to moderate in chronic forms, acute cases can be serious, if not fatal, and nearly all severe acute GVHD prominently involves the gastrointestinal tract, which can drive activation of pathogenic T cells and potentially lead to tissue damage following allo-HCT.
Systemic corticosteroids are standard first-line treatment for acute GVHD. However, response rates generally range only from 40% to 60%, and there are concerns of side effects. Meanwhile, second-line treatments are of inconsistent benefit.
With previous studies on mice showing benefits of targeting Notch pathway inhibition, particularly DLL4, Dr. Maillard and colleagues further investigated the effects in nonhuman primates that were allo-HCT recipients, using the anti-DLL4 antibody REGN421, which has pharmacokinetic and toxicity information available from previous studies.
The nonhuman primates were treated with one of two dosing regimens: a single dose of REGN421 3 mg/kg at baseline, post HCT, (n = 7) or three weekly doses at days 0, 7 and 14, post transplant (n = 4). Those primates were compared with 11 primates receiving allo-HCT transplants that received supportive care only.
Primates receiving three weekly doses of REGN421 showed antibody concentrations of greater than 2 mcg/mL for more than 30 days post HCT. A single dose of REGN421 was associated with protection from acute GVHD at day 0, while three weekly doses showed protection at day 0, 7, and 14, consistent with an impact of REGN421 during the early phases of T-cell activation.
Compared with animals receiving only supportive care, prophylaxis with REGN421 was associated with delayed acute GVHD onset and lengthened survival.
Of the 11 primates treated with REGN421, none developed clinical signs of gastrointestinal acute GVHD, whereas the majority of those receiving standard care or other preventive interventions did.
“Detailed analysis of acute GVHD clinical presentations in REGN421-treated animals in comparison to no treatment controls revealed near complete protection from GI-acute GvHD with REGN421,” the authors reported.
Furthermore, pathology scores in the gastrointestinal tract were lower with REGN421 treatment, compared with the no-treatment cohort, and the scores matched those of healthy nontransplanted nonhuman primates.
The primates treated with REGN421 did ultimately develop other clinical and pathologic signs of skin, hepatic or pulmonary acute GVHD, but without gastrointestinal disease.
The treatment was not associated with any adverse effects on the allo-HCT, with primates receiving either a single dose or three weekly doses of REGN421 showing rapid donor engraftment after allo-HCT, including high bone marrow, whole blood, and T-cell donor chimerism.
“Reassuringly, short-term systemic DLL4 blockade with REGN421 did not trigger unexpected side effects in our nonhuman primate model, while preserving rapid engraftment as well hematopoietic and immune reconstitution.”
The mechanism preserving the engraftment, described as a “major surprise,” specifically involved DLL4 inhibition blocking the homing of pathogenic T cells to the gut while preserving homing of regulatory T cells that dampen the immune response, Dr. Maillard explained.
“This effect turned out to be at least in part through a posttranslational effect of DLL4/Notch blockade on integrin pairing at the T-cell surface,” he explained. “This was a novel and quite unexpected mechanism of action conserved from mice to nonhuman primates.”
The results are encouraging in terms of translating to humans because of their closer similarities in various physiological factors, Dr. Maillard said.
“The nonhuman primate model of transplantation [offers] a transplantation model very close to what is being performed in humans, as well as the opportunity to study an immune system very similar to that of humans in nonhuman primates,” he said.
Dr. Maillard noted that, while trials in humans are not underway yet, “we are in active discussions about it,” and the team is indeed interested in testing REGN421 itself, with the effects likely to be as a prophylactic strategy.
There are currently no approved anti-DLL4 antibody drugs for use in humans.
“Our approach is mostly promising as a preventive treatment, rather than as a secondary treatment for GVHD, because DLL4/Notch blockade seems most active when applied early after transplantation during the time of initial seeding of the gut by T cells (in mice, we had observed the critical time window for a successful intervention to be within 48 hours of transplantation),” Dr. Maillard said.“There remain questions about which other prophylactic treatments we should ideally combine anti-DLL4 antibodies with.”
Dr. Maillard has received research funding from Regeneron and Genentech and is a member of Garuda Therapeutics’s scientific advisory board.