A New Era of Cancer Immunotherapy: Breakthroughs, Challenges, and the Path Forward

For decades, cancer treatment relied on surgery, chemotherapy, and radiation—treatments that often harm healthy cells alongside cancerous ones. Today, cancer immunotherapy has revolutionized care by harnessing the body’s own immune system to fight tumors. Drugs like immune checkpoint inhibitors (ICIs) have turned some terminal cancers into manageable conditions, offering long-term survival to patients once given months to live. But while immunotherapy has opened a new chapter in oncology, it’s not a cure-all. Many patients don’t respond, and others develop resistance over time.

In a 2021 review published in the Chinese Medical Journal, researchers Ri-Lan Bai, Nai-Fei Chen, Ling-Yu Li, and Jiu-Wei Cui (from the Cancer Center at the First Hospital of Jilin University) break down the breakthroughs, challenges, and promising solutions shaping the future of immunotherapy. Their work highlights how scientists are tackling the field’s biggest hurdles—from drug resistance to patient heterogeneity—to make immunotherapy more effective for more people.

The Breakthroughs: How Immunotherapy Changed Cancer Care

Immunotherapy works by reactivating the immune system, which cancer often suppresses to grow unchecked. The most successful class of immunotherapies—immune checkpoint inhibitors (ICIs)—target proteins like PD-1 (on T cells) and PD-L1 (on tumor cells) that act as “brakes” on the immune response. By blocking these proteins, ICIs allow T cells to recognize and kill cancer cells.

The results have been transformative:

Durable responses: For some patients with melanoma, lung cancer, or kidney cancer, ICIs have led to complete remission—meaning no detectable cancer—even years after treatment.
Wider access: Drugs like pembrolizumab (Keytruda) and nivolumab (Opdivo) are now standard first-line treatments for several cancers, including non-small cell lung cancer (NSCLC) and melanoma.
Combination success: Trials like KEYNOTE-189 showed that combining pembrolizumab with chemotherapy improved survival for NSCLC patients regardless of PD-L1 expression—a marker once thought critical for response.

But as Bai et al. note, “relatively few patients with advanced cancer experience life-altering durable survival.” The immune system is complex, and tumors are masterful at evading it.

The Challenges: Why Immunotherapy Doesn’t Work for Everyone

Three key hurdles limit immunotherapy’s impact:

1. Resistance: Primary and Acquired

Most patients either never respond to immunotherapy (primary resistance) or initially improve but later worsen (acquired resistance). Tumors use clever tactics to evade the immune system:

Adaptive resistance: A tumor “learns” to counter immune attacks—for example, by upregulating other checkpoint proteins (like LAG-3 or TIM-3) when PD-1 is blocked.
Intrinsic resistance: Tumors may lack “neoantigens” (mutant proteins that the immune system recognizes as foreign) or have defective antigen-presenting cells (APCs) that fail to alert T cells to cancer.

2. The Tumor Immune Microenvironment (TIME): A Hostile Terrain

The TIME—the ecosystem of cells, molecules, and blood vessels around a tumor—plays a huge role in immunotherapy success. Tumors often create an immunosuppressive microenvironment by:

Recruiting regulatory T cells (Tregs) or myeloid-derived suppressor cells (MDSCs) that dampen T cell activity.
Producing cytokines like TGF-β or adenosine that suppress immune responses.
Growing abnormal blood vessels that prevent T cells from entering the tumor.

Bai et al. explain that the TIME can be categorized into three types:

Immune-inflamed: T cells are present and active (best for ICIs).
Immune-excluded: T cells are stuck outside the tumor (ICI-resistant).
Immune-desert: Few to no T cells (ICI-resistant).

3. Lack of Predictive Biomarkers

No single test can reliably predict who will respond to immunotherapy. While PD-L1 expression (measured via biopsy) is used clinically, it’s imperfect: some patients with high PD-L1 don’t respond, and others with low PD-L1 do. Other markers like tumor mutational burden (TMB) or tumor-infiltrating lymphocytes (TILs) show promise but aren’t yet standard.

Overcoming Resistance: Targeting the TIME and Beyond

To make immunotherapy work for more patients, researchers are focusing on two strategies: reprogramming the TIME and combining therapies to hit tumors from multiple angles.

1. Understanding the TIME to Personalize Treatment

By analyzing the TIME, doctors can tailor treatment to a patient’s tumor. For example:

Immune-excluded tumors: Drugs that “normalize” blood vessels (like anti-angiogenics) can help T cells enter the tumor.
Immune-desert tumors: Cancer vaccines or adoptive cell therapies (like CAR-T cells) can introduce tumor-specific T cells where none existed.

A 2018 study of 10,000 tumors (Thorsson et al.) identified six TIME subtypes—from “wound-healing” to “TGF-β-dominant”—each requiring different treatments. This kind of precision could transform how we match patients to therapies.

2. Combination Therapies: Boosting Efficacy by Working Together

Combining immunotherapies with other treatments is the most promising way to overcome resistance. Bai et al. highlight several game-changing combinations:

ICI + Chemotherapy or Radiotherapy

Chemotherapy can kill cancer cells and release tumor antigens, making it easier for T cells to recognize cancer. The KEYNOTE-189 trial found that pembrolizumab plus chemotherapy doubled survival for metastatic NSCLC patients compared to chemotherapy alone.

Radiotherapy works similarly: it destroys tumors while activating the immune system. A 2020 pooled analysis (Theelen et al.) showed that adding pembrolizumab to radiotherapy improved outcomes for metastatic lung cancer patients.

ICI + Anti-Angiogenic Drugs

Tumors grow abnormal blood vessels that block T cells and fuel immunosuppression. Anti-angiogenic drugs (like bevacizumab or lenvatinib) “normalize” these vessels, allowing T cells to infiltrate and ICIs to work better. A 2018 study (McDermott et al.) found that combining the ICI atezolizumab with bevacizumab prolonged survival for renal cell carcinoma patients by 50%.

Bispecific Antibodies: Targeting Two Pathways at Once

Bispecific antibodies (bsAbs) are engineered to bind two targets—for example, PD-L1 (on tumors) and TGF-β (a immunosuppressive cytokine). Drugs like bintrafusp alfa (M7824) trap TGF-β while blocking PD-L1, creating a more favorable TIME. Early trials show promise in NSCLC and other cancers.

ICI + Cellular Immunotherapy

CAR-T cells (genetically modified T cells that target cancer antigens) and NK cells (natural killer cells) can fill the gap for “non-inflamed” tumors. A 2020 study (Lin et al.) found that combining pembrolizumab with allogeneic NK cells improved survival for advanced NSCLC patients compared to pembrolizumab alone.

Precision Medicine: Finding the Right Treatment for the Right Patient

The future of immunotherapy lies in precision medicine—using biomarkers to match patients to treatments. Bai et al. highlight key advances:

PD-L1: The “Gold Standard” (For Now)

PD-L1 expression on tumor cells is the most widely used biomarker. Trials like KEYNOTE-024 showed that pembrolizumab works best for NSCLC patients with PD-L1 ≥50%, while KEYNOTE-042 expanded access to patients with PD-L1 ≥1%.

TMB: A Marker for “Mutant” Tumors

Tumor mutational burden (TMB)—the number of mutations in a tumor—predicts how well ICIs work. Tumors with high TMB (≥10 mutations/Mb) have more neoantigens, making them easier for the immune system to target. In 2020, the FDA approved pembrolizumab for any solid tumor with high TMB that has progressed after other treatments.

Gut Microbiota: A Surprising Player

Recent research shows that the gut microbiome influences immunotherapy response. Patients with “good” bacteria (like Bifidobacterium) are more likely to respond to ICIs, while those with “bad” bacteria (like Enterococcus) are not. Fecal microbiota transplantation (FMT) is being tested to “reset” the microbiome and boost ICI efficacy.

The Future: Novel Delivery Systems and Clinical Trial Innovations

Even with better combinations and biomarkers, immunotherapy faces one more challenge: toxicity. ICIs can cause severe side effects when the immune system attacks healthy tissue. To fix this, researchers are developing targeted delivery systems that send drugs directly to tumors or immune cells.

Nanotechnology: Tiny Carriers, Big Impact

Nanoparticles—particles 1,000 times smaller than a human hair—can deliver ICIs, cytokines, or vaccines to the TIME without harming healthy cells. For example:

Membrane-coated nanoparticles: These mimic immune cells to evade the body’s defenses and target tumors. A 2018 study (Zhang et al.) used PD-L1-expressing nanoparticles to block PD-1 and activate dendritic cells, leading to durable anti-tumor responses in mice.
Exosome-mimetic nanovesicles: Derived from M1 macrophages (pro-inflammatory immune cells), these nanovesicles repolarize tumor-associated macrophages (TAMs) from “pro-tumor” to “anti-tumor.” A 2018 study (Choo et al.) found that combining these nanovesicles with anti-PD-L1 therapy reduced tumor size more than either treatment alone.

Innovative Clinical Trials

Traditional clinical trials are slow and expensive. To speed up drug development, researchers are using:

Umbrella trials: Test multiple drugs in patients with the same tumor type (e.g., NSCLC) based on biomarkers.
Basket trials: Test one drug in patients with different tumors that share a genetic marker (e.g., high TMB).
Platform trials: Continuously add or remove treatments based on real-time data, allowing faster adaptation to new findings.

Conclusion: A Collaborative Path to Curing Cancer

Immunotherapy has already saved millions of lives, but its full potential remains untapped. Bai et al.’s review makes one thing clear: overcoming immunotherapy’s challenges will require collaboration—between basic scientists studying the TIME, clinicians testing combination therapies, and engineers developing targeted delivery systems.

The future of cancer care is personalized, precise, and patient-centered. With advances in biomarkers, combination therapies, and nanotechnology, we’re closer than ever to turning “cancer” into a manageable condition—even a curable one. As the authors note: “Coping with these challenges requires the joint efforts of clinicians and scientists… to accelerate the understanding of the complex interactions between cancer and immunity.”

For patients and families, this means hope: hope that the next breakthrough will be the one that works for them. And for the scientific community, it means a shared mission: to turn the promise of immunotherapy into a reality for everyone.

doi.org/10.1097/CM9.0000000000001490

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