CRISPR Gene Editing Puts Researchers Closer to an
“Off-the-Shelf” CAR T-Cell Product for ALL
Last year marked the first U.S. Food and Drug Administration
approvals of autologous T-cell immunotherapies for the
treatment of cancer, including acute lymphocytic leukemia
(ALL) and non-Hodgkin lymphoma (NHL). However, several
challenges have limited the clinical development of chimeric
antigen receptor (CAR) T-cell therapies against T-cell malig-
nancies, including difficulties harvesting non-malignant
autologous T cells from affected patients. Allogeneic,
off-the-shelf CAR T-cell products would overcome some
of these limitations, but the shared expression of target
antigens between effector cells and malignant cells can
lead to “self-killing” of CAR T cells.
Researchers at the Washington University School of Medicine
in St. Louis have developed a new CAR T-cell strategy using the
gene-editing technology CRISPR/Cas9 to engineer “fratricide-
resistant” CAR T cells. Lead author Matthew L. Cooper, PhD,
and colleagues published their results in Leukemia. 1 The
preclinical data from this mouse model demonstrates the fea-
sibility of an allogeneic strategy to treat T-cell malignancies.
“Cancerous T cells and healthy T cells have exactly the
same protein – CD7 – on their surfaces, so if we program
T cells to target CD7, they would attack both the cancerous
cells and each other, thus undermining this approach,” senior
author John F. DiPersio, MD, PhD, explained. 2 “To prevent
this T-cell fratricide, we used CRISPR/Cas9 gene editing to
remove CD7 from the CAR T cells, so they no longer carry
the target.” CD7 was also selected because this antigen could
be deleted in T cells without affecting immune function, the
investigators noted.
”[With this approach,] we
could collect T cells from
any healthy donor and
have the gene-edited
T cells ready in advance.”
—MATTHEW L. COOPER, PhD
The researchers generated the CD7-CAR product,
UCART7, using CRISPR/Cas9 gene editing and T-ALL cells
collected from patients being treated at their institution.
Then, they tested this approach in mice xenografted with
either T-ALL cell lines or primary cells from human T-cell
ALL lines. The xenografted mice were randomized to receive
either UCART7 or UCART19, an allogeneic T cell product
directed against CD19 (expressed on B-cells, not T cells) that
served as a negative control. Mice received CAR T-cell doses
at 2×10 6 /kg.
Following transduction of T cells, the investigators
observed significantly fewer UCART7 cells than UCART19
cells. UCART7 cells were biased toward a CD4 phenotype,
compared with UCART19. Mice receiving UCART7 had
significantly prolonged survival and reduced tumor burden,
compared with mice receiving UCART19 (p=0.0003).
Also, mice treated with the gene-edited T cells targeted to
CD7 survived 65 days, compared with 31 days for those that
received CD19 targeted cells (p=0.0003).
The investigators then tested the capacity of UCART7 to
kill primary T-ALL in vivo without inducing an alloreactive
graft-versus-leukemia effect or xenogeneic graft-versus-host
disease (GVHD). T-ALL blasts were absent in peripheral
blood of mice receiving UCART7, compared with those
receiving UCART19 (p<0.0001). UCART7 recipients also
had normal-sized spleens, while those receiving UCART19
exhibited splenomegaly.
“These UCART7 cells efficiently kill human T-ALL cell
lines and patient-derived primary T-ALL in vitro and in vivo
without resulting in xenogeneic [GVHD],” the researchers
wrote of their findings, indicating that CD7 is a candidate for
gene editing of CAR T cells. “Should rejection occur, UCART7
would still provide a viable bridge to transplantation, which
many feel is the primary benefit of [CAR T-cell therapy].”
“[An] additional benefit of this approach is that a patient
could receive this therapy much more quickly after diagnosis,”
said Dr. Cooper. “We wouldn’t need to harvest the patient’s
own T cells and then modify them, which takes time. We also
wouldn’t have to find a matched donor. We could collect T cells
from any healthy donor and have the gene-edited T cells ready
in advance.”
The study is limited by its use of mice and will need to be
validated in a human model. Studies are underway to assess
the viability of scaling UCART7 for clinical trials.
The authors report no financial conflicts.
REFERENCES
1. Cooper ML, Choi J, Staser K, et al. An “off-the-shelf” fratricide-resistant
CAR-T for the treatment of T cell hematologic malignancies. Leukemia. 2018
February 20. [Epub ahead of print]
2. Washington University School of Medicine in St. Louis press release, March
5, 2018.
May 2018
5