Herpes simplex virus type-1 amplicon vectors for vaccine generation in acute lymphoblastic leukemia

Abstract

For leukemia vaccine generation, high-efficiency gene transfer is required to express immunomodulatory molecules that stimulate potent antileukemic immune responses. In this context, herpes simplex virus type-1 (HSV-1)-derived vectors have proven to be a promising tool for genetic modification of lymphoblastic leukemia cells. Yet, vector-associated viral protein expression might inadvertently modulate vaccine efficacy facilitating both immune evasion and immune stimulation. To explore the issue of immune-stimulation versus immune-suppression in immature lymphoblastic leukemia cells, two types of HSV-1 amplicon vectors, helper virus-dependent and helper virus-free that express the immunomodulatory molecules CD70 and IL-2, were compared with regard to their vector-associated immunomodulatory potential. We first established that lymphoblastic cell lines and primary acute lymphoblastic leukemia (ALL) cells express HSV receptor genes. Lymphoblastic cell lines were transduced with high efficiency, and in primary ALL cells high gene transfer rates of 47715 and 42714% were obtained with helper virus-dependent and -free HSV-1 amplicon vectors, respectively. The efficacy of the two amplicon vectors to induce antineoplastic responses was assessed in a vaccine setting in mice with pre-existing highly malignant lymphoblastic disease. Treatment of mice with vaccine cells transgenically expressing CD70+IL2 significantly suppressed lymphoblastic cell proliferation and improved survival. Of note, when helper virus-dependent HSV-1 amplicon vectors were used for vaccine preparation, the high immunogenic potential of the vector itself, in the absence of transgenic CD70+IL2 expression, seemed to be sufficient to mediate protection comparable to the antineoplastic response achieved by expression of immunomodulatory molecules. Thus for vaccine generation in B lymphoblastic leukemia, the immunogenic potential of HSV-1 helper virus-dependent amplicon vectors does provide additional benefit to the high transduction efficiency of HSV-1-derived vectors.

HSV as a vector in vaccine development and gene therapy

“…176,177 HSV amplicon vectors have also been evaluated as cancer vaccines by expressing combinations of cytokines and immunomodulatory proteins for treatment of a variety of experimental tumors. 24,175,[178][179][180][181] A promising, new approach to cancer is the selective degradation of mRNA by RNA interference (RNAi) 182 or interference with microRNAs that support tumor growth. 183 HSV amplicon vectors expressing siRNAs have been used recently to mediate posttranscriptional silencing of EGFR, which is frequently activated in human…”

Effect of promoter strength on protein expression and immunogenicity of an HSV-1 amplicon vector encoding HIV-1 Gag

“…Among the appealing characteristics of these vectors are their large insert capacity, favorable safety profile and broad cellular/tissue tropism -which extends to antigen presenting cells, such as dendritic cells (DC) [3]. As a result, helper-free HSV-1 amplicons encoding mammalian or microbial proteins can elicit strong, antigenspecific immune responses, and may have utility in a range of applications, including cancer treatment and prophylactic vaccination against pathogens such as human immunodeficiency virus type-1 (HIV-1) [3][4][5][6][7][8][9][10].…”

Amplicons as Vaccine Vectors

“…In these experiments, the vaccine formulation consisted of irradiated A20 cells that had been transduced with amplicon stocks in vitro, and which were then administrated s.c. to the mice. Vaccine cells expressing both IL-2 and CD70 significantly inhibited lymphoblastic tumor growth; the helper-free and helper-containing stocks were equally effective [Zibert et al, 2005]. Interestingly, when helper-containing amplicon stocks were used for the vaccine preparation, an equivalent level of protection was also obtained with an "empty" amplicon vector (lacking IL-2 or CD70).…”

“…A recent study by Zibert and colleagues also used helperfree amplicons, and compared their effectiveness with that of matched helper-containing amplicons in the setting of acute lymphoblastic leukemia (ALL) [Zibert et al, 2005]. In these studies, amplicon vectors encoding either IL-2 or the costimulatory ligand CD70 were constructed, and then packaged using either a helper-free system or a helper virus (the IE3 deleted recombinant virus, d120).…”