SCID mouse

Photo courtesy of NCI

SAN DIEGO—A novel xenograft model of acute myeloid leukemia (AML) demonstrated that the JAK/STAT inhibitor ruxolitinib can prevent severe cytokine release syndrome (CRS) without impairing the anti-tumor effect of chimeric antigen receptor (CAR) T cells, according to research presented at the 2016 ASH Annual Meeting.

Almost all patients responding to CART-cell therapy develop CRS, and up to 60% develop severe CRS.

The research team believes the mouse model and findings with ruxolitinib will provide an important platform for studying CRS prevention and treatment.

At ASH, Saad Kenderian, MD, of the Mayo Clinic in Rochester, Minnesota, explained that CRS produces very high levels of the inflammatory protein IL-6.

Treatment with ruxolitinib in clinical studies has reduced human inflammatory cytokines. Therefore, it made sense to the investigators to study ruxolitinib as a means to prevent CRS after CAR T-cell therapy.

Tocilizumab has been used to treat grade 3 and 4 CRS, but physicians are concerned that earlier introduction during the course of CRS may impair CAR T-cell function.

At present, no relevant preclinical model for CRS after CAR T-cell therapy exists, “which is limiting the development of CRS preventative modalities that could, in turn, enhance the feasibility of CAR T-cell therapy,” Dr Kenderian said.

And so the investigators decided to create an animal model.

Dr Kenderian described the work at the meeting as abstract 652.

Mouse model for human CRS

Using NSG-S mice (non-obese diabetic, SCID ɣ -/- mice additionally transgenic for human stem cell factor, IL-3, and GM-CSF), investigators injected them with blasts from AML patients. After 3 to 4 weeks, investigators treated the mice with 1 x 10⁶ CD123-directed CAR T cells.

Dr Kenderian noted this dose of CART123 was 10 times higher than doses previously used in primary AML xenograft models.

The mice became weak, emaciated, developed hunched bodies, became withdrawn, had poor motor responses, and died in 7 to 10 days. The illness started within 1 week of CAR T-cell injection and correlated with significant expansion of T cells in the peripheral blood of these mice.

The team studied the serum from these mice 7 days after CART123 injection. They found extreme elevation of human IL-6, interferon-γ, tumor necrosis factor-α, and other inflammatory cytokines. This response resembled human CRS after CAR T-cell therapy.

Ruxolitinib treatment

The investigators first studied ruxolitinib activity in vitro with CART123 cells and found that ruxolitinib did not impair CAR T-cell effector functions.

“And also, ruxolitinib was not directly toxic to CAR T cells,” Dr Kenderian added.

But ruxolitinib did slow CAR T-cell proliferation in vitro.

They next tested ruxolitinib and CART123 in the mouse model.

Once the mice experienced high-burden disease, investigators treated them with CART123. That same day, investigators began treating the mice with ruxolitinib for 1 week. The mice were randomized to 30, 60, 90 mg/kg, or vehicle twice a day.

Twenty-nine days after AML injection, the mice treated with CART123 plus 90 mg or 60 mg of ruxolitinib experienced less weight loss than those treated with CART123 plus 30 mg of ruxolitinib or CART123-only.

“And more importantly, all mice had eradication of their disease,” Dr Kenderian said.

Mice treated with CART123 plus 90 mg, 60 mg, or 30 mg of ruxolitinib or CART123 alone had fewer AML blasts at day 28 than mice treated with 60 mg of ruxolitinib alone.

The investigators then analyzed the effect of ruxolitinib on the anti-tumor effect of CART123 and found that ruxolitinib did not impair it.

The attenuation of inflammatory cytokines translated to a survival advantage for mice treated with CART123 and ruxolitinib.

The investigators believe the addition of ruxolitinib to CAR T-cell therapy is a modality that should be investigated in patients at high-risk of developing CRS.

Dr Kenderian disclosed patents, royalties, and research funding from Novartis.

Ruxolitinib may prevent CRS after CAR T-cell therapy