Passage
Proteins known as cancer/testis antigens (CTAs) are normally expressed exclusively in germline cells but may become reactivated in cancer cells due to chromatin remodeling (eg, gene activation due to DNA demethylation) . Because of their normally restricted expression, CTAs can elicit an immune response when expressed by cancer cells derived from other tissue types. Several CTAs are known to inhibit apoptosis or promote cell division in cancer cells, making them more resistant to traditional chemotherapy. Accordingly, cancer research instead has focused on immunotherapy treatments targeting CTAs.In a study, researchers isolated peripheral blood lymphocytes (B lymphocytes, T lymphocytes, natural killer [NK] cells) from two healthy individuals. These lymphocytes were cultured with signaling factors known to promote helper T cell (T_h cell) proliferation. After 7 days, cultures from both individuals were enriched for T_h cells, which expressed proteins generally involved in activating other lymphocytes. A subset of the cultures from each individual was treated with 5-Aza-CdR, a DNA-demethylating agent. Reverse transcription polymerase chain reaction (RT-PCR) was used to analyze expression of several CTAs (ie, MAGEs) in both untreated and 5-Aza-CdR-treated lymphocyte cultures, as well as in untreated melanoma (skin cancer) and breast cancer cell lines (Figure 1) . GAPDH, a protein expressed in most cell types, served as a control.
Figure 1 Gels showing RT-PCR results for MAGE expressionAdditional peripheral blood lymphocytes were isolated from the same healthy individuals and incubated with the T_h cells that had been treated with 5-Aza-CdR. After 11 days, these cultures consisted primarily of an increased number of NK cells and cytotoxic T lymphocytes (CTLs) . Researchers found that these CTLs were able to induce apoptosis in breast cancer cell lines but did not affect healthy cells.Researchers used a similar procedure to induce CTL proliferation in lymphocytes isolated from a breast cancer patient. The CTLs were then incubated with cells obtained from a biopsy of the patient's cancerous tissue. Following this experiment, researchers found that apoptosis was induced in the patient's cancer cells.
Kirkin et al. Adoptive cancer immunotherapy using DNA-demethylated T helper cells as antigen-presenting cells. Nature Communications. 2018; 9:785
-CTLs incubated in the absence of 5-Aza-CdR-treated T_h cells were unable to induce apoptosis in the cancer cells described in the passage. Given this, which of the following statements best describes why the 5-Aza-CdR-treated T_h cells were necessary to induce proliferation of functional CTLs?

Question

Passage
Proteins known as cancer/testis antigens (CTAs) are normally expressed exclusively in germline cells but may become reactivated in cancer cells due to chromatin remodeling (eg, gene activation due to DNA demethylation) . Because of their normally restricted expression, CTAs can elicit an immune response when expressed by cancer cells derived from other tissue types. Several CTAs are known to inhibit apoptosis or promote cell division in cancer cells, making them more resistant to traditional chemotherapy. Accordingly, cancer research instead has focused on immunotherapy treatments targeting CTAs.In a study, researchers isolated peripheral blood lymphocytes (B lymphocytes, T lymphocytes, natural killer [NK] cells) from two healthy individuals. These lymphocytes were cultured with signaling factors known to promote helper T cell (T_h cell) proliferation. After 7 days, cultures from both individuals were enriched for T_h cells, which expressed proteins generally involved in activating other lymphocytes. A subset of the cultures from each individual was treated with 5-Aza-CdR, a DNA-demethylating agent. Reverse transcription polymerase chain reaction (RT-PCR) was used to analyze expression of several CTAs (ie, MAGEs) in both untreated and 5-Aza-CdR-treated lymphocyte cultures, as well as in untreated melanoma (skin cancer) and breast cancer cell lines (Figure 1) . GAPDH, a protein expressed in most cell types, served as a control.

Figure 1 Gels showing RT-PCR results for MAGE expressionAdditional peripheral blood lymphocytes were isolated from the same healthy individuals and incubated with the T_h cells that had been treated with 5-Aza-CdR. After 11 days, these cultures consisted primarily of an increased number of NK cells and cytotoxic T lymphocytes (CTLs) . Researchers found that these CTLs were able to induce apoptosis in breast cancer cell lines but did not affect healthy cells.Researchers used a similar procedure to induce CTL proliferation in lymphocytes isolated from a breast cancer patient. The CTLs were then incubated with cells obtained from a biopsy of the patient's cancerous tissue. Following this experiment, researchers found that apoptosis was induced in the patient's cancer cells.
Kirkin et al. Adoptive cancer immunotherapy using DNA-demethylated T helper cells as antigen-presenting cells. Nature Communications. 2018; 9:785
-CTLs incubated in the absence of 5-Aza-CdR-treated T_h cells were unable to induce apoptosis in the cancer cells described in the passage. Given this, which of the following statements best describes why the 5-Aza-CdR-treated T_h cells were necessary to induce proliferation of functional CTLs?

Quizplus · Accepted Answer

11ecba2d_1042_0793_a3bf_936fc42bf664_MD0008_00 Helper T cells (T_h cells) are specialized adaptive immune cells that generally bind foreign antigens presented by surface antigen-presenting proteins (ie, MHC proteins) on other immune cells and release cytokines (signaling molecules) that enhance immune cell activity. Commonly, cytotoxic T lymphocytes (CTLs) are activated by binding foreign antigens displayed by antigen-presenting immune cells (eg, dendritic cells) and receiving activation signals from both the antigen-presenting cell and T_h cells. As the passage states, researchers successfully cultured T_h cells that expressed proteins that activate other lymphocytes. Treatment of these T_h cells with the DNA demethylating agent 5-Aza-CdR caused them to express several cancer/testis antigens (CTAs), as shown in Figure 1. Accordingly, these T_h cells could likely act as antigen-presenting cells and display CTA fragments for binding by inactive CTLs. Signaling molecules from these T_h cells could then activate CTLs, inducing the proliferation of CTLs able to cause apoptosis of CTA-expressing cancer cells. The question states that CTLs incubated in the absence of 5-Aza-CdR-reated T_h cells were unable to induce apoptosis in cancer cells. This finding is most likely attributed to the fact that CTLs must receive signals from other immune cells (eg, antigen-presenting cells and T_h cells) to become activated. (Choice A) Generally, CTLs must receive signals from other immune cells (not cancerous or pathogen-infected cells) to become activated and proliferate into functional CTLs. (Choice B) T lymphocytes are initially produced in the bone marrow before being transported to the thymus, a specialized lymphoid organ where T lymphocyte maturation occurs. There a process called negative selection eliminates any T lymphocytes that recognize self-antigens (ie, those that would induce apoptosis in healthy cells). Negative selection is carried out by thymic cells (not T_h cells) and would not affect the function of CTLs able to recognize foreign antigens (eg, CTAs). (Choice D) Healthy CTLs recognize and bind foreign antigens but do not express them. Expression of antigenic proteins by CTLs would most likely cause them to be targeted and destroyed by other immune cells. Educational objective: Cytotoxic T lymphocytes require signals from other immune cells such as antigen-presenting cells (eg, dendritic cells) and T_h cells to proliferate into active immune cells that can induce apoptosis in cancerous or pathogen-infected cells.

Passage Proteins Known as Cancer/testis Antigens (CTAs) Are Normally Expressed Exclusively