Quite similar to infection with HSV-1 (herpes simplex virus type 1).

WHO estimates that 67% of people below 50 are infected worldwide. Still, you don't see 2 of 3 people regularly developing cold sores.

Infection with a pathogen does not necessarily mean showing signs of disease.

Our body does not have a defense mechanism against ionizing radiation, that is true. Though, we do have countermeasures against its effects.

DDR, or DNA-damage-response, is a cluster of measures cells regularly deploy to restore DNA damage caused by radiation, amongst others. They are not without failure, which is why cancer exists. Nevertheless, these processes are exceedingly powerful when it comes to restoring defective DNA. Without them, cancer would be more frequent by several orders of magnitude.

Might simply be an error in the print or result from oversimplification. Happens even with the most reviewed books and manuscripts.

You are 100% accurate with your assessment. The only thing keeping you from understanding is an assumption you made involuntarily (which also is kind of non-trivial).

You select for neomycin-resistance, but not by adding neomycin. Instead, to select eukaryotic cells you would use a substance called geneticin or G418 which is toxic to eukaryotic cells, but cleared by the neomycin-resistance gene.

The immune system is very adapt in recognizing foreign biological matter like bacteria, viruses and even another eucaryote organism's cells.

On the other hand, the body selects it's own immune cells for low responsiveness to its own proteins to prevent autoimmunity.

Cancer is essentially constituted of a body's very own cells gone aberrant. That means, these cells usually share several of the following characteristics:

• Internally and/or externally unregulated growth, proliferation, and expansion
• Loss of tissue function
• Migration to neighbouring tissues
• Denial of internal and/or external apoptotic stimuli (self-destruction)
• Evasion of immune cell recognition
• Inhibition of immune cell signalling

To break it down in terms of your question: cancer cells are naturally less likely to be targeted by immune cells than external pathogens, as they are basically a body's own cells. Immune cells, nevertheless, will kill wildly aberrant cells rapidly. That basically means cancer cells are naturally selected for variants that circumvent this line of defense. Either, they lose receptors by which they are primarily recognized by immune-cells, or gain/upregulate mechanisms by which they suppress immune cell-responses despite proper recognition.

Now, mRNA vaccines can reverse these effects by different mechanisms. You could potentially use them to

• increase the expression of receptors the immune cells use naturally
• decrease the expression of receptors inhibiting immune cell response
• introduce new epitopes the body knows how to react to, like surface proteins of a bacterium

All of these increase efficiency, efficacy and precision of the immune cell response against the targeted tumor cell.

Your question is hard to answer for several reasons, mostly because you do not define what unique traits you mean. Also, it is hard to assess your level of knowledge in chemistry and physics.

I would argue that mostly it is not due to any packaging effects.

As a biochemist, I consider carbon to be unique mostly because of its nuclear makeup, meaning its position in the periodic table. As first member of main-group 4 it is a relatively small, abundant atom that is capable of forming a variety of different bonds. Meaning sp1-hybridized single bonds, sp2-hybridized double bonds and sp3-hybridized triple bonds. On the other hand, its mediocre electronegativity of 2,5 makes it possible for C to bond with a variety of different other elements more or less stably.

These factors allow for carbon to be perfect as base for organic chemistry under terrestrial conditions - meaning the diverse chemistry of life.

Metal bonds are a bit out of my area of expertise, as I am a biochemist and usually only encounter metals in my field sporadically.

Maybe someone in anorganic chemistry or material science can give us their view here? And please do correct me if I'm wrong.

As far as I understand, metal bonds are in a way similar to ionic bonds, in that bonding electrons are completely ripped from their atoms, but do not reside with the ion that took them. Rather, they are distributed and moveable throughout a crystal structure of the ions.

As to the question if metal alloys are classified mixtures - I do not know. I am inclined to believe they are not, but as I said, metal chemistry is beyond my area of expertise. Edit: u/passerculus elaborated on the nature of metal bonds. Refer to their comment for info about that, rather than my half knowledge!

I'd like to elaborate on that a bit regarding some important types of bonds and molecular interactions. I'll try to simplify as much as I can and proceed from weakest to strongest in terms of bonding strength.

Van-der-Waals-Force The weakest of the underlying forces are Van-der-Waals-forces. They occur between any kind of atom and/or molecule and are weakly attractive across small distances, until they become repulsive when atoms or molecules are pushed together too tightly.

Dipole interactions Molecules, which are basically arrangements of semi-permanently bound atoms, can have complex structures, depending on how many atoms are involved and how they are arranged. Based on that complexity, some areas of them will have a electromagnetic charge (positive or negative, just like a battery). Charged regions of a molecule will attract molecule regions of the opposite charge.

Hydrogen-bonds Hydrogen bonds are basically a special form of dipole interactions. In specific arrangements inside molecules, hydrogen (partially positively charged) and oxygen (partially negatively charged) will get into close contact and start attracting each other strongly because of their polarity. The term hydrogen bond, is a bit misleading, as this is not considered a bond that would form a new molecule, but one of the weaker interactions between molecules. However, it is such a common interaction, that giving it its own term is reasonable. These bonds, together with dipole interactions, are what make water (highly polar) dissolve other polar molecules, while oil (non polar) does not mix well with water.

Covalent bonds At this point, we are at what you would consider a bond formed by a chemical reaction. They appear when polar interactions like the ones before are so strong, that they start to rip on what composes atoms. An atom has a core, which contains neutral parts (neutrons) and positive parts (protons), as well as a shell of electrons, which are negatively charged. When a pull between two atoms is strong enough, one will start tugging on the electrons of the other. That leads to an arrangement, at which the electron basically belongs to both of them, forming a covalent bond. We call that a reaction, the result of which is a combination of two atoms that form a unison with new characteristics - a molecule (in contrast to everything up to this point, which would result in mixing but not an alteration of involved substances e.g. a reaction)

Ionic bonds As you can imagine, you can step up that scenario once more. If atom A is so strong, that it overpowers atom B in the tug of war, it can completely rip the electron from B. The result of this are two so-called ions. One, that lacks one piece of its internal negative charges, making it positively charged in total. The other one gained an internal negative charge in form of an electron and hence becomes overall negatively charged. What again happens is an attraction between negative and positive, pulling the two ions together and forming what is called an ionic bond, that in and on itself is even stronger than a covalent bond, as the difference in charges is much, much higher than in any bond I mentioned before.

TL;DR - a reaction requires an interaction force altering the structural composition of an atom or molecule. Mixing two compounds does not necessarily produce forces strong enough to do so.