Page 440 - Williams Hematology ( PDFDrive )

414 Part V: Therapeutic Principles Chapter 26: Immune Cell Therapy 415

restricting allele. Moreover, it can be difficult to achieve the same surface V H V H
level of TCR expression in transduced T cells as observed in the parental Recognition
T-cell clone from which the TCR genes were isolated. This problem was module V L V L Variable spacer
apparent in the first clinical trial in which MART-1 TCR-engineered T Transmembrane
cells were used to treat melanoma and the low TCR expression likely region
contributed in part to the limited antitumor activity of the TCR-modified CD28, 4-1BB, OX40
149
T cells. Another problem is that the TCR transfer endows T cells Signaling module/
costimulation
with additional rearranged TCR chains, leading to T cells that could CD3z
potentially express four different TCR molecules on the cell surface: the
natural endogenous TCR, the exogenously introduced TCR, and two Figure 26–4. Structure of a chimeric antigen receptor (CAR). The CAR
mixed heterodimers consisting of endogenous and exogenous TCR is typically composed of a recognition module that is fused in tandem
chains. Such mismatched TCRs could result in potentially deleteri- to nonsignaling extracellular and transmembrane domains and intracel-
lular signaling elements. The recognition module, spacer domain, and
150
ous self-reactive specificities. This problem can be mitigated by the signaling modules of the CAR can be modified to optimize tumor cell
introduction of cysteine residues into the extracellular constant region recognition and T-cell function.
of the introduced α and β TCR chains to provide for disulfide bond for-
mation 151,152 or by using murine constant domains in place of the human
constant regions, both of which promote preferential pairing of the signaling T-cell effector function. 94–96,163,164 CARs typically consist of
153
introduced chains. More recently, strategies to knock out or silence the a single-chain variable fragment (scFV) derived from the V and V
H
L
endogenous TCR have been developed. 154,155 These modifications pro- sequences of a mAb specific for a tumor cell-surface molecule, fused
vide for more stable pairing during assembly and export, and better to a trans-membrane domain, as well as the CD3ζ-signaling domain
competition for limiting components of the TCR complex. 156 alone, or in combination with one or more costimulatory signaling
Strategies to enhance the potency of the TCR, such as by enhancing modules, such as CD28,4–1BB, OX40, or CD27 (Fig. 26–4). 94–96,165,166
TCR affinity, may increase the risk of toxicity, particularly if self-antigens CARs can be introduced into T cells by gene transfer to target surface
are targeted. 157–161 In a clinical trial, autologous T cells were modified molecules expressed on tumors. Unlike conventional TCRs, CARs are
to express optimized high-affinity MART-1 or gp100 TCR transgenes not MHC-restricted and have the advantage that a single construct can
and transferred to 36 melanoma patients. Nine of the patients exhibited be used to treat all patients expressing the tumor antigen.
clinical antitumor responses, but “on-target” toxicities to normal mela- A large number of CARs targeting a variety of molecules expressed
nocytes in the skin, eye, and ear that required local glucocorticoid treat- on hematologic malignancies have been developed. 96,167,168 Examples for
ment were observed in a significant fraction of patients that received candidate targets for the treatment of hematologic malignancies include
the high-avidity TCR. In a separate trial, autologous T cells modified CD19, CD20, and the orphan tyrosine kinase receptor ROR1 170–172
157
96
169
to express a high-affinity TCR specific for the carcinoembryonic anti- expressed on B-cell lymphomas and leukemias; Lewis Y, CD44v6,
173
174
gen (CEA) were transferred to three patients with colorectal cancer. The CD33 and/or CD123 expressed on acute myeloid leukemia 168,175–177 ;
serum CEA levels decreased in all three patients and there was some and NKG2D ligands or the B-cell maturation antigen (BCMA)
179
178
regression of metastatic disease. However, the clinical trial was closed expressed on myeloma.
early when all three patients developed severe colitis, putatively from Efficient methods for T-cell activation, gene transfer, and expan-
recognition of normal epithelial cells that express CEA. Toxicity was sion of T cells for therapy have been developed and the results of pilot
161
also observed in a study in which nine cancer patients were treated clinical trials of T cells modified to express CARs specific for CD19,
with autologous T cells modified to express an anti–MAGE-A3 TCR. CD20, ERBB2, the disialoganglioside GD2, and mesothelin have been
Five patients experienced cancer regression, but three patients experi- reported and provided evidence of in vivo antitumor activity. 180–187
enced serious and/or fatal neurologic toxicity. This occurred because However, serious toxicity has also been observed including a fatal toxic-
of previously unrecognized expression of MAGE-A12, which encodes ity shortly after infusion of a single high dose of ERBB2-specific CAR-T
the identical epitope, in the human brain that resulted in neuronal cell cells that contained both CD28 and 4–1BB costimulatory domains, and
160
destruction. Additional safety concerns of targeting MAGE-A3 using was attributed to cytokine release and recognition of normal lung epi-
an affinity-enhanced TCR construct were identified after an unex- thelium that expresses low amounts of ERBB2. Toxicity to normal tis-
188
pected fatal cardiac toxicity. Detailed analysis showed cross-reactivity sues was also observed in patients receiving CAIX CAR-engineered T
of the engineered MAGE-A3 TCR-modified T cells with a titin-derived cells for the treatment of metastatic renal cell carcinoma. 189,190
peptide. 158,159 The most encouraging results with CAR-T cells have been obtained
Such serious “on-target and off-target” toxicities of TCR gene targeting the B-cell lineage-restricted CD19 molecule that is expressed
transfer suggested that targeting antigens with restricted expression on on B-cell leukemias and lymphomas. Dramatic and durable remissions
tumor cells such as mutant epitopes or cancer testes antigens is pref- in patients with chronic lymphatic leukemia (CLL) and acute lymphatic
erable. NY-ESO-1 is expressed in many human cancers, but not in leukemia (ALL) have been reported after infusion of autologous T cells
normal tissues, except testis. A TCR specific for an HLA-A2-restricted transduced with CD19-specific CARs that contained either a CD28
NY-ESO-1 epitope was used for the treatment of melanoma and syno- or a 4–1BB costimulatory domain. 182,183,191,192 In these studies, infused
162
vial sarcoma. Toxicity was not observed, and encouraging results T cells were shown to expand in vivo, induce tumor lysis and a defi-
showed that the TCR-engineered T cells mediated objective responses ciency of normal CD19+ B cells, and persist long-term in some patients.
in four of six patients with synovial cell carcinoma and five of 11 mela- The complete response rate appears to be higher in patients with ALL
noma patients. than those with CLL or lymphoma for reasons that have not been elu-
cidated. Tumor regression is often associated with a cytokine release
Genetic Retargeting of T Cells with Chimeric Antigen syndrome (CRS) initiated by activation of CAR-T cells in vivo, associ-
Receptors ated with elevated levels of IFN-γ, IL-6, and tumor necrosis factor, and
A notable advance in T-cell therapy has been the development of CARs resulting in high fever, hypotension, and neurologic abnormalities. 183,193
that link recognition domains of antibodies to molecules involved in CRS is more severe in patients with high tumor burden and can require

Kaushansky_chapter 26_p0409-0420.indd 415 9/17/15 6:01 PM