Page 1195 - Clinical Immunology_ Principles and Practice ( PDFDrive )

1160 ParT TEN Prevention and Therapy of Immunological Diseases

Salmonella and BCG infections outside of North America. Defects was obtained, gamma-retroviral vectors were constructed and
in gp91phox encoded by CYBB account for the most common shown to correct several manifestations of the disorder in patient
X-linked form of CGD while the remaining defects are inherited derived cells and in murine models. However, it is not fully
19
in an autosomal recessive (AR) pattern. Since its initial descrip- known what levels of WAS transgene expression are needed to
tion almost six decades ago, CGD has evolved from a disease safely and effectively correct the major manifestations of
with early mortality to one with relatively good outcomes and lymphocyte and platelet dysfunction. A concern has been raised
multiple treatment options. that sub-optimal levels or low frequency of expression of WAS
While prophylactic antimicrobial and immunomodulatory protein (WASP) could allow auto-immunity to develop. If
agents have dramatically decreased infection rates in CGD patients, correction is only partial, (e.g., some proportion of B cells are
curative therapy can only be achieved with HSCT. Transplant not gene corrected and have defective auto-regulatory function),
outcomes have continued to improve over the years, with good auto-immunity may occur. 16
results reported even in patients with high-risk features such as A first trial of gene therapy for WAS used a gamma-retroviral
intractable infections and auto-inflammation using reduced- vector with a very potent long terminal repeat promoter enhancer
13
intensity conditioning protocols. Nevertheless, allogeneic HSCT (from the Spleen Focus Forming Virus). G-CSF-mobilized
can still be complicated by graft-versus-host disease and pre- peripheral blood stem cells were used as the HSC source and
existing infections and is not preferred for those without an conditioning with myeloablative dosages of busulfan was given
HLA-matched stem cell donor. For these patients, autologous prior to transplant. There were excellent initial results in terms
HSCT with gene-modified cells is becoming a more viable and of immune reconstitution and platelet counts, demonstrating
realistic option. that gene therapy can be therapeutic for this disorder. However,
The first gene therapy trials for CGD began in the mid-1990’s there was subsequently a very high incidence of acute leukemia
again using gamma-retroviral vectors. As with ADA SCID, initial among these patients, developing within a few years from treat-
trials in which pre-transplant conditioning was not used did ment, with ALL, AML or both occurring in a shocking 7 of 9
17
not lead to efficacy as there was minimal if any engraftment subjects. The mechanism of insertional oncogenesis from the
of gene-corrected stem cells. In subsequent studies where gamma-retroviral vector was clearly the cause, with the leukemias
non-myeloablative conditioning with busulfan was used, showing clonal vector integrations adjacent to known proto-
increasingly higher levels of engraftment of corrected stem oncogenes, such as LMO2 and MDS1.
cells was achieved. The best and worst of these studies was one While that trial was being initiated, work was ongoing through
using a gammaretroviral vector with a potent transcriptional a multi-center collaboration in the EU to develop a SIN lentiviral
control element to drive high level expression of the gp91phox vector for WAS that uses the promoter from the WAS gene per
gene. The three treated subjects had initial development of se to drive expression of the WAS cDNA. Extensive pre-clinical
neutrophils with restored oxidase function and cleared severe studies showed the efficacy of this vector to improve immunologic
resistant infections. However, insertional oncogenesis occurred and hematologic parameters in murine and human disease
in this study also, and myelodysplasia or frank myeloid leukemia models. 18,19 And, it displayed significantly lower risks for geno-
developed. More recently, trials are using a lentiviral vector with a toxicity than the type of gamma-retroviral vector used in the
myeloid-specific transcriptional control element intended to drive first trial.
gp91phox expression in mature myeloid cells, where it is needed, The lentiviral vector with the WAS promoter has now been
but to not have activity in HSCs that are the likely targets for used in parallel but independent phase I/II clinical trials per-
transformation. Initial results are showing safety and evidence of formed in several countries. 20,21 Relatively high intensity condition-
efficacy. 14 ing was administered to attempt to obtain high-level engraftment
Recently, the group at NIH has also investigated the use of of gene-corrected HSCs, with some differences among the centers
site-specific endonucleases (a zinc-finger nuclease, discussed in the precise conditioning regimen used. All used moderate
below) to target integration of a normal gp91phox cDNA expres- doses of busulfan (pharmacokinetically [pK]-adjusted) and
15
sion cassette to the AAVS1 gene “safe harbor site”. Good levels fludarabine, and variably, rituximab or other serotherapy agents.
of engraftment were demonstrated in mouse models, with up These trials have uniformly demonstrated efficacy and safety.
to 11% of human cell expressing gp91phox in vivo. This work Findings have included clinical improvement in general health,
represents the first step towards targeted gene editing for X-CGD bleeding incidents, and eczema, and as expected for an autologous
and suggests that it can also be possible to integrate the transgene transplant, no problems from graft versus host disease. Most
in its natural location in the genome under control of its have had good recovery of T, B, NK cell numbers and functions.
endogenous promoter. However, there has been only modest and variable improvements
for platelet levels (e.g. 20-60,000/uL), with evidence that higher
WISKOTT-ALDRICH SYNDROME (WAS; transplanted dose of transduced cells led to higher platelet
20
Chapter 35) counts. No new onset of auto-immunity has been reported,
although in some cases pre-existing problems have persisted. In
The Wiskott Aldrich Syndrome (WAS), initially described as fact, decreases of indices of auto-immunity and improved B cell
22
an X-linked syndrome in kindreds in Germany and the US, tolerance have been documented after gene therapy for WAS.
presents with multiple clinical manifestations, including the Polyclonal vector integration patterns were seen, with no reported
classical triad of immune deficiency, eczema and thrombocy- development of clonal expansions or frank leukoproliferative
topenia. The complex immune deficiency involves defects of T, complications. Integration site patterns resemble those seen in
B, NK and antigen-presenting cells. The identified WAS gene other trials using lentiviral vectors into human HSCs, with highly
encodes a 501 amino acid proline-rich protein that has multiple diverse vector integration sites and no predilection for cancer-
identified functional domains, placing it at the nexus of intracel- related genes, significantly different than the pattern seen in the
lular signaling and cytoskeleton control. Once the WAS cDNA gamma-retroviral vector trials.