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GRAPEVINE, TEXAS—Adding specialized T cells to allogeneic bone marrow transplants can prevent graft-vs-host disease (GVHD) while preserving the graft-vs-tumor (GVT) effect, preclinical research suggests.

Donor-derived CD4+ invariant natural killer T cells (iNKT cells) helped protect mice from developing GVHD and lymphoma, thereby improving their survival.

As human CD4+ iNKT cells can be expanded in vitro, these findings may translate to the clinic, said study investigator Dominik Schneidawind, MD, of Stanford University in California.

Dr Schneidawind discussed this research at the 2014 BMT Tandem Meetings as abstract 2*, which was designated one of the meeting’s “Best Abstracts.”

Improved survival

Dr Schneidawind and his colleagues created a model of allogeneic bone marrow transplant in Balb/c (H-2Kd) mice. The mice were first irradiated with 8 Gy and then received T cell-depleted bone marrow, along with 1 x 106 CD4/CD8 T cells (Tcon) from C57Bl/6 (H-2Kb) donor mice and varying doses of CD4+ iNKT cells: 1 x 104 to 1 x 105.

Mice that received 100,000 CD4+ iNKT cells had significantly improved survival (P=0.002)—and better weight and GVHD scores—compared to mice that received bone marrow grafts alone. But a CD4+ iNKT dose as low as 10,000 cells also conferred a significant improvement in survival (P=0.03).

“In contrast, you need roughly 500,000 to 1 million donor-derived regulatory T cells to achieve a comparable survival benefit in this model of bone marrow transplantation,” Dr Schneidawind noted.

GVT effect

Dr Schneidawind and his colleagues also evaluated the impact of CD4+ iNKT cells on the GVT effect. They used luciferase-transfected BCL1 cells to induce lymphoma development, injecting the cells into mice 1 day before transplant.

Mice that received BCL1 cells, with or without CD4+ iNKT cells, showed increasing bioluminescence imaging (BLI) signals and all died from progressive lymphoma. The mice that received BLC1 and Tcon did not show an increase in BLI signals, but they all died from GVHD.

However, the mice that received BCL1, Tcon, and CD4+ iNKT cells didn’t show any sign of lymphoma or GVHD and survived through the whole experiment (P=0.002).

The investigators conducted the same experiment with the luciferase-positive A20 cell line. And they observed similar results. Mice that received A20 cells, Tcon, and CD4+ iNKT cells showed no sign of lymphoma and had significantly improved survival (P=0.002) over animals that received A20 and Tcon.

“Interestingly, animals that received A20 cells and 50,000 CD4+ iNKT cells only, without Tcon, showed a significant decrease in BLI signal and significantly improved survival,” Dr Schneidawind noted.

“So we conclude from these experiments that CD4+ iNKT cells do not abrogate the Tcon-mediated [GVT] effect but might exert some distinct antitumor activity by themselves.”

Mechanism of GVHD prevention

Lastly, Dr Schneidawind and his colleagues wanted to determine exactly how CD4+ iNKT cells prevent GVHD. The group’s experiments showed that the cells inhibit the proliferation of alloreactive T cells and promote the expansion of donor-derived CD4+ FoxP3+ Tregs.

The investigators decided to take a closer look at the Tregs, evaluating their role in GVHD-related death.

To do this, the team evaluated survival in 4 groups of mice: (1) irradiated controls; (2) mice that received only bone marrow; (3) mice that received Tcon, CD4+ iNKT cells, and a graft depleted of CD4+ FoxP3+ Tregs; and (4) mice that received Tcon, CD4+ iNKT cells, and a non-depleted graft.

“Animals that received a Treg-depleted graft and were treated with CD4+ iNKT [plus Tcon] did not show a significant improvement in survival [over controls],” Dr Schneidawind said.

“In contrast, animals that received a Treg-non-depleted graft showed a significant improvement in survival [P=0.006]. So we conclude that the expansion of these Tregs is necessary to protect from GVHD lethality and that they are required in this context.”

In closing, Dr Schneidawind noted that, although human CD4+ iNKT cells are rare, they can be isolated from peripheral blood and expanded in vitro. This suggests his group’s findings might ultimately prove useful for patients. ht-logo-end

*Information in the abstract differs from that presented.

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