Beyond Deletions and Additions: Engineering Longevity in Pig Organs with Multi-Gene Editing

The Limitations of Current Xenotransplantation Edits

Today’s CRISPR-edited pig organs primarily rely on two strategies:

1. Deleting problematic pig genes (e.g., CMAH to remove immunogenic sugars).
2. Adding human genes (e.g., CD46 to block immune attacks).

While these edits have extended organ survival from hours to months, they fail to address a critical issue: biological aging. Pig organs — like all mammalian tissues — deteriorate over time due to cellular senescence, telomere shortening, and oxidative stress. Even if immune rejection is controlled, the transplanted organ may still degenerate prematurely.

Why Target Aging Genes?

The pig CDKN2A gene (encoding p16INK4a) is a key regulator of cellular aging. By knocking it out — while also adding longevity-enhancing genes like TERT (telomerase) — we can:

• Delay senescence (cells remain functional longer).
• Improve stress resistance (organs tolerate ischemia/reperfusion injury better).
• Extend graft lifespan beyond current 6–12 month limits.

Comparison: Single Edits vs. Longevity Engineering

CMAH Knockout (Simple Deletion)

Pros:

• Removes major immune target (Neu5Gc sugar).
• Reduces hyperacute rejection.
• Technically easier (single edit)

Cons:

• Doesn’t stop other immune attacks.
• Pig organs still age normally.
• Short-term solution (fails in months).

CD46 Addition (Human Gene Insertion)

Pros:

• Actively blocks immune destruction (complement system).
• Works alongside CMAH knockout.
• Proven in trials (~6-month survival).

Cons:

• Doesn’t prevent T-cell rejection.
• No effect on organ aging.
• Requires precise targeting.

CDKN2A Knockout + TERT (Aging Control)

Pros:

• Slows cellular aging (organs last longer).
• Complements immune edits.
• Potential for decades-long function.

Cons:

• Complex (needs multiple edits).
• Risk of cancer if overexpressed.
• Not yet tested in large animals.
• CMAH knockout

How to Design This in Benchling

Step 1: Find the Pig Gene You Want to Edit

1. Search for:

• Pig CDKN2A (aging gene): Try ENSSSCG000000XXXXX
• Human TERT (anti-aging gene): Search NM_198253 (human telomerase).

1. Click “Import” to save them to your project.

Step 2: Design CRISPR Guides to Cut the Pig Gene

1. Open the pig CDKN2A sequence.
2. Click CRISPR”.
3. Pick a 20-bp guide RNA (gRNA) near the gene’s start (look for ATG). Example:
4. Check:

• On-target score (green if ≥70).
• Off-target score (red if ≤50 is safe).

Step 3: Add the Human Anti-Aging Gene

1. Assemble:

• A promoter (e.g., EF1α to turn on the gene everywhere).
• The human TERT gene (from Step 1).
• A terminator (e.g., WPRE to stabilize the gene).

Name it: “TERT_Cassette”.

Step 4: Combine with Immune Edits

1. Repeat Steps 1–3 for:

• CMAH knockout (delete pig sugar gene).
• CD46 addition (human shield gene).

1. Use “Assembly” to stitch all parts into one big DNA blueprint.

Step 5: Check for Mistakes

1. Click “Translate” on your final design.

• Red stops = Bad (unexpected breaks in proteins).
• Long green bar = Good (full-length proteins).

1. Click “Off-Target Analysis” to avoid cutting wrong genes.

Why This Beats Simple Edits

1. Synergistic Effects

• CMAH/CD46 prevent immune rejection.
• CDKN2A/TERT combat aging.

1. Clinical Impact:

• Organs could last years, not months.
• Reduces need for re-transplantation.

Challenges

• Delivery Complexity: Requires multiple gRNAs + large HDR templates.
• Safety: Must avoid unintended consequences (e.g., cancer risk from TERT).

The Road Ahead

The next phase of xenotransplantation isn’t just about evading the immune system — it’s about building organs that survive as long as their human hosts. By integrating aging research with CRISPR engineering, we’re one step closer to truly permanent solutions.

Key Takeaway: While CMAH knockout and CD46 addition were revolutionary first steps, the future lies in multi-gene circuits that address rejection and longevity. Benchling’s design tools make this complex editing feasible — but the real test will come in primate trials.

About the Author

Hello! My name is Vedant Ravilla, I am currently a grade 10 high school student and I have a fascination for the medical line. My dream is to one day become a doctor ( specifically an obstetric anesthesiologist). Currently, I am enrolled in White Oaks Secondary School (WOSS) — a high school located in Ontario, Canada; Apart from my academics, I spend most of my spare time learning about emerging technologies applied in medical settings. Feel free to contact me through my email; ravillavedant@gmail.com