Later Mahayana Buddhists were concerned with the transcendent aspect of the Dharma.
So therefore if the Dharma is transcendental, totally beyond space and time, then so is the Dharmakaya.
One response to this was the development of the Tathagatagarbha Doctrine.
Another was the introduction of the Sambhogakaya which conceptually fits between the rupakaya, now renamed nirmanakaya or created Body, and the Dharmakaya.
The Sambhogakaya is that aspect of The Buddha, or the Dharma, that one meets in visions and in deep Meditation.
It could be considered an interface with the Dharmakaya.
What it does, and what the Tathagatagarbha Doctrine also does, is bring the transcendental within reach, it makes it immanent.