CAR-T GENE THERAPY WITH LENTIVIRAL AND GAMMA-RETROVIRAL VECTORS MAY INCREASE THE RISK OF INFECTIONS

Nicoletti M. CAR-T gene therapy with lentiviral and -retroviral vectors may increase the risk of infections.  International Journal of Infection. 2025;9(2):53-56.

M. Nicoletti^*

Department of Public Health and Infectious Diseases, Sapienza University of Rome, Italy.

*Correspondence to:
Prof. Mauro Nicoletti,
Department of Public Health and Infectious Diseases,
Sapienza University of Rome,
Rome, Italy.
e-mail: mauro.nicoletti@uniroma1.it

ABSTRACT

Chimeric antigen receptor T cell (CAR-T) therapy uses viral vectors such as lentiviruses and g-retrovirals that are used in to insert genetic material into host cells. The vectors must possess certain characteristics that allow them to be effective without harming the host cell. g-retroviral vectors that are derived from the murine leukemia virus act on already activated cells. Lentiviral vectors are derived from the human immunodeficiency virus (HIV)-1 and carry out transduction on both proliferating T lymphocytes and on quiescent, non-activated T lymphocytes. The drugs tisagenlecleucel and axicabtagene ciloleucel are currently approved for CAR-T gene therapy. The modified T cells from patient’s express an anti-CD19 CAR receptor and attack tumor B cells that express CD19, destroying them. However, this treatment induces the production of inflammatory cytokines, and neurotoxicity, especially when axicabtagene ciloleucel is used. Among the side effects with this therapy is immunosuppression that favors the onset of infections. The inhibition of immunity occurs both on the production of immunoglobulins and on phagocytosis, favoring the proliferation of microorganisms such as viruses, bacteria, and fungi. It can be concluded that despite the efficacy of CAR-T therapy, side effects are still a problem to be resolved.

KEYWORDS: Chimeric antigen receptor T cell, CAR-T therapy, lentiviral vector, g-retroviral vector, gene therapy

INTRODUCTION

The study of virology and human immunodeficiency virus (HIV)-1 has been instrumental in the development of novel therapies (1). Lentiviral and g-retroviral vector therapy have aroused much interest in the scientific community and could hold great therapeutic promise (2). These therapies consist of inserting a new gene into the DNA of the abnormal cell to compensate for the non-functioning or absent one.

Gene therapy is now being applied in the treatment of incurable genetic diseases, and these therapies raise great hopes for their treatment, even if the side effects are not yet fully understood (3). The method of replacing the diseased gene(s) with a healthy one begins with the collection of stem cells from the patient’s bone marrow carrying the switched-off or absent gene, which is then put into culture. A vector virus carrying the healthy gene is inserted into these cells, generating a genetic transformation (4). The modified cells are then re-inoculated into the blood of the patient who has the gene defect. The vectors carrying the healthy gene can be lentiviral or g-retroviral.

In chimeric antigen receptor T cell (CAR-T) gene therapy, lentiviral and g-retroviral vectors are important to transfer therapeutic genes into the patient’s T lymphocytes (5). In gene therapy, vectors must have certain characteristics, such as acting on target cells, having stability in integration, having a low degree of oncogenic risk, having simple and inexpensive production, and allowing a wide clinical use of CAR-T (6). Lentiviral vectors are currently preferred for most CAR-T therapies due to their greater efficiency and relative safety. g-retroviral vectors are less suitable for CAR-T therapy and carry a slightly higher risk of insertion, which can prove toxic. However, both vectors have been essential to the history and development of ex-vivo gene therapies, particularly in modifying T lymphocytes to combat various diseases that respond poorly to current therapies, including cancer.

DISCUSSION

In gene therapy, the first viral vectors used were retrovirals, mainly derived from the Moloney murine leukemia virus (7). These vectors integrate well into the genome and exert a long duration on the transplanted gene. In addition, g-retroviral vectors have a preference for activated T cells, which are necessary in CAR-T therapy (8). However, g-retroviral vectors are not able to exert transduction in non-activated resting cells, and this can sometimes be a disadvantage. Furthermore, gene insertion could potentially occur near oncogenes causing mutagenesis and tumors (9).

In recent years, there has been growing interest in the application of CAR-T cells not only in cancer, but also in chronic and resistant viral infections. This research is still in the preclinical phase; however, CAR-T cells are being studied for various resistant and chronic viral infections. For example, in acquired immunodeficiency syndrome (AIDS), the primary goal is to eliminate HIV-infected CD4+ cells, as well as the macrophages that serve as reservoirs of the virus. CAR-T cells recognize the viral envelope proteins gp120 that are expressed on infected cells and eliminate them in combination with anti-retroviral therapies (ART). However, infected cells may express low levels of antigen, making them difficult to recognize. In Epstein-Barr Virus (EBV), CAR-T cells can also be directed against viral proteins expressed by EBV-positive transformed cells (such as LMP1 and LMP2), while anti- cytomegalovirus (CMV) CAR-T cells are being studied in CMV infections.

Lentiviral vectors are derived from HIV-1 but are non-pathogenic (10). They exert transduction on both proliferating T cells and resting non-activated T cells (11). These vectors exert stable and long-term integration on the CAR genome and reduce the risk of reactivation and recombination. The limitation of the use of lentiviral vectors is due to their high cost, and since they derive from HIV, they require great care in their use (12).

Tisagenlecleucel and axicabtagene ciloleucel using CAR-T are approved for gene therapy today. These drugs utilize slow viral or g-retroviral vectors based on the biological characteristics of the patient (13). Both tisagenlecleucel (brand name Kymriah) and axicabtagene ciloleucel (brand name Yescarta) are made from the patient’s own (autologous) T cells that have been genetically modified to express an anti-CD19 CAR receptor, targeting B tumor cells (14). The choice of vector must be made based on the type of cell, safety, regulation, required duration of expression, and costs.

However, there are important differences between the two compounds. At the clinical level, Tisagenlecleucel exerts a greater persistence of CAR-T cells over time, while axicabtagene ciloleucel gives a faster and shorter-lasting response (15).

Tisagenlecleucel is used for B-cell acute lymphoblastic leukemia in patients over 25 years of age, while axicabtagene ciloleucel has been approved for follicular lymphoma in relapsed or refractory cases (16).  However, both treatments can cause side effects such as cytokine release syndrome and can cause neurotoxicity (17). It seems that treatment with axicabtagene ciloleucel, compared to that with tisagenlecleucel, is faster and has a greater effect in triggering the production of pro-inflammatory cytokines and inducing neurotoxicity since it acts on CD28 (18).

CAR-T therapy is an advanced form of immunotherapy primarily used to treat certain types of blood cancers such as leukemia and lymphoma (19).  While this therapy is very effective in some patients, it also carries risks, including a significantly increased risk of infections (20). The risk of increased infections with CAR-T therapy may depend on lymphodepletion before therapy, since before the infusion of the CAR-T cells, the patient receives chemotherapy necessary to reduce the number of lymphocytes (21).  This is to create space for the CAR-T cells, generating immunosuppression (22).

CAR-T cells targeting CD19 (as in B-cell lymphoma therapies) also react against healthy B cells, reducing their number and causing hypogammaglobulinemia, which leads to infections by microorganisms (23). CAR-T therapy also induces a reduction in the number of neutrophils, elements necessary for bacterial phagocytosis, the immune system’s first step against microbial infections (24).

In addition, in the case in which pro-inflammatory cytokines are induced by CAR-T treatment, the therapeutic use of corticosteroids to reduce inflammation can lead to the inhibition of the immune system and increase vulnerability to infections (25). The most common infections that can occur during treatment with CAR-T therapy are bacterial, viral, and fungal (26).  Bacterial infections occur mainly in the first 30 days of treatment, with pneumonia and urinary tract and blood infections (26).  Viral infections can be due to reactivation of latent viruses such as Herpes simplex and zoster, CMV, respiratory syncytial virus (RSV), influenza, and adenovirus.  Fungal infections such as aspergillosis and candidiasis are less common and are due to neutropenia.

CONCLUSIONS

CAR-T therapy uses viral vectors such as lentiviruses and g-retroviruses. Tisagenlecleucel and axicabtagene ciloleucel are two drugs that have currently been approved for CAR-T gene therapy. Although CAR-T therapy is a promising treatment, attention needs to be focused on reducing potential negative side effects, such as the production of inflammatory cytokines, neurotoxicity, and immunosuppression that favors infections by microorganisms.

Conflict of interest

The author declares that they have no conflict of interest.

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